A Criticism of the Cell-Theory; being an Answer to Mr. Sedgwick's ...
A Criticism of the Cell-Theory; being an Answer to Mr. Sedgwick's ...
A Criticism of the Cell-Theory; being an Answer to Mr. Sedgwick's ...
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A OEITIOISM OF THE GULL-THEORY. 137<br />
A <strong>Criticism</strong> <strong>of</strong> <strong>the</strong> <strong>Cell</strong>-<strong>Theory</strong>; <strong>being</strong> <strong>an</strong> <strong>Answer</strong><br />
<strong>to</strong> <strong>Mr</strong>. <strong>Sedgwick's</strong> Article on <strong>the</strong> Inadequacy<br />
<strong>of</strong> <strong>the</strong> <strong>Cell</strong>ular <strong>Theory</strong> <strong>of</strong> Development.<br />
By<br />
Gilbert C. Bourne, M.A., F.L.S.,<br />
Fellow <strong>of</strong> New College, Oxford.<br />
"Jedes Lebendige isb kein Einzelnes, sondern ein Melirheit; selbst ins<strong>of</strong>ern<br />
es uns als Individuum erscheint, bleibt es doch eine Yersammlung you<br />
lebendigen, selbst<strong>an</strong>digen Wesen, die der Idee, der Anlage nach gleich sind,<br />
in der Erscheinung aber gleich oder ahnlich, ungleich oder unahnlich werdea<br />
Iconncn. Diese Wesen sind <strong>the</strong>its urspriinglich schon verbunden, <strong>the</strong>ils finden<br />
und vereinigen sie sich. Sie entzweien sicb und suclien sich wieder, und<br />
bewirken so eine unendliche Production auf alle Weise und nach alien<br />
Seiten."—GOETHE (1807).<br />
MR. ADAM SEDGWICK has <strong>of</strong> late thrown himself with<br />
considerable zeal in<strong>to</strong> <strong>the</strong> part <strong>of</strong> a zoological iconoclast, <strong>an</strong>d<br />
has displayed <strong>an</strong> evident relish in battering <strong>the</strong> idols which,<br />
he would fain make us believe, are turning away <strong>the</strong> minds <strong>of</strong><br />
men from <strong>the</strong> true faith, <strong>of</strong> which <strong>the</strong>re are but few orthodox<br />
exponents. Nor may we blame him for his fervour, for <strong>an</strong> old<br />
faith always emerges purer, if not firmer, from <strong>the</strong> ordeal <strong>of</strong><br />
sharp <strong>an</strong>tagonism. The idols in question are <strong>the</strong> developmental<br />
law <strong>of</strong> von Baer <strong>an</strong>d <strong>the</strong> cell-<strong>the</strong>ory.<br />
Seeing how import<strong>an</strong>t a thing it is that a science should be<br />
guided by principles capable <strong>of</strong> <strong>being</strong> expressed in precise<br />
l<strong>an</strong>guage, it has been a matter <strong>of</strong> surprise <strong>to</strong> me that some<br />
competent person has not taken up <strong>the</strong> challenges which<br />
<strong>Mr</strong>. Sedgwick has thrown down. For, if his views are <strong>to</strong><br />
pf evail, two <strong>of</strong> <strong>the</strong> fundamental principles <strong>of</strong> zoology, principles<br />
which have hi<strong>the</strong>r<strong>to</strong> directed <strong>an</strong>d steadied <strong>the</strong> course <strong>of</strong> zoological<br />
speculation, are taken away from us; <strong>an</strong>d unless some
138 . GILBERT 0. BOURNE.<br />
better <strong>an</strong>d more distinct principles are put in <strong>the</strong>ir place, <strong>the</strong><br />
course <strong>of</strong> speculation may be expected <strong>to</strong> be very erratic<br />
indeed. It is not without serious misgivings as <strong>to</strong> my own<br />
competence that I, in default <strong>of</strong> a better champion, take up<br />
one <strong>of</strong> <strong>the</strong>se challenges, <strong>an</strong>d I propose <strong>to</strong> criticise <strong>Mr</strong>. <strong>Sedgwick's</strong><br />
recent article on <strong>the</strong> inadequacy <strong>of</strong> <strong>the</strong> cellular <strong>the</strong>ory<br />
<strong>of</strong> development, leaving for a future occasion <strong>the</strong> consideration<br />
<strong>of</strong> his earlier article on von Baer's law.<br />
It is <strong>to</strong> be regretted that <strong>Mr</strong>. Sedgwick should, in putting<br />
forward a view aflFecting one <strong>of</strong> <strong>the</strong> fundamental propositions<br />
<strong>of</strong> biology, have chosen <strong>to</strong> adopt a controversial method, which<br />
c<strong>an</strong>not but have <strong>the</strong> effect <strong>of</strong> weakening his case. And it is<br />
still more a pity that he should be so unsparing in abuse <strong>of</strong><br />
his imaginary opponents, whilst he himself commits <strong>the</strong> very<br />
fault for which he so much blames <strong>the</strong>m. For he lays, in <strong>the</strong><br />
front <strong>of</strong> his indictment, a charge <strong>of</strong> vagueness <strong>an</strong>d unsubst<strong>an</strong>tiality<br />
against <strong>the</strong> supporters <strong>of</strong> <strong>the</strong> cellular <strong>the</strong>ory.<br />
" We are dealing," he says, " with a kind <strong>of</strong> ph<strong>an</strong><strong>to</strong>m which<br />
takes different forms in different men's eyes. There is a w<strong>an</strong>t<br />
<strong>of</strong> precision about <strong>the</strong> cell-ph<strong>an</strong><strong>to</strong>m, as <strong>the</strong>re is also about <strong>the</strong><br />
layer-ph<strong>an</strong><strong>to</strong>m, which makes it very difficult <strong>to</strong> lay ei<strong>the</strong>r <strong>of</strong><br />
<strong>the</strong>m. Nei<strong>the</strong>r <strong>of</strong> <strong>the</strong>se <strong>the</strong>ories c<strong>an</strong> be stated in a m<strong>an</strong>ner<br />
satisfac<strong>to</strong>ry <strong>to</strong> every one. The result is that it is not easy <strong>to</strong><br />
bring ei<strong>the</strong>r <strong>of</strong> <strong>the</strong>m <strong>to</strong> book."<br />
I shall show, later on, that this charge <strong>of</strong> vagueness is not<br />
al<strong>to</strong>ge<strong>the</strong>r justified; what I am at present concerned with is<br />
<strong>to</strong> show that <strong>Mr</strong>. Sedgwick is as much open <strong>to</strong> <strong>the</strong> charge <strong>of</strong><br />
vagueness as <strong>the</strong> rest <strong>of</strong> <strong>the</strong> zoological world which he castigates.<br />
Read his article through as carefully as one may, one<br />
c<strong>an</strong>not find <strong>an</strong>y definite or precise statement <strong>of</strong> his own st<strong>an</strong>dpoint,<br />
saving that he quotes passages from one <strong>of</strong> his earlier<br />
works. The critic, <strong>the</strong>refore, mnst be content <strong>to</strong> infer<br />
from <strong>the</strong> tenor <strong>of</strong> <strong>the</strong> whole article, <strong>an</strong>d from particular<br />
passages in it, as well as from his previous writings, what<br />
<strong>Mr</strong>. Sedgwick does or does not believe with regard <strong>to</strong> <strong>the</strong> cell<strong>the</strong>ory,<br />
<strong>an</strong>d if he is misinterpreted, it is his own fault.
A CRITICISM OP THE DELL-THEORY. 139<br />
It is probably a fair summary <strong>of</strong> his position <strong>to</strong> say that, for<br />
<strong>the</strong> present, he limits his objections <strong>to</strong> <strong>the</strong> application <strong>of</strong> <strong>the</strong><br />
cell-<strong>the</strong>ory <strong>to</strong> <strong>the</strong> process <strong>of</strong> growth during embryonic development<br />
j but that he scarcely conceals his preference for <strong>the</strong><br />
view that <strong>the</strong>re are no such things as discrete cells in <strong>the</strong><br />
so-called multicellular org<strong>an</strong>ism. And as it is necessary, at<br />
<strong>the</strong> outset, <strong>to</strong> have a perfectly clear idea <strong>of</strong> his me<strong>an</strong>ing, I will<br />
quote passages from <strong>the</strong> work <strong>to</strong> which he refers in his opening<br />
paragraph, assuming that what he stated <strong>the</strong>n he is prepared<br />
<strong>to</strong> adhere <strong>to</strong> now, <strong>an</strong>d that his last article is intended <strong>to</strong><br />
emphasise <strong>the</strong> views which he formerly propounded, <strong>an</strong>d <strong>to</strong><br />
bring fresh evidence in support <strong>of</strong> <strong>the</strong>m.<br />
On p. 204 <strong>of</strong> <strong>the</strong> second part <strong>of</strong> his account <strong>of</strong> <strong>the</strong> development<br />
<strong>of</strong> <strong>the</strong> Cape species <strong>of</strong> Peripatus, he says:—"It is<br />
becoming more <strong>an</strong>d more clear every day that <strong>the</strong> cells composing<br />
<strong>an</strong>imal tissues are not isolated units, but that <strong>the</strong>y are<br />
connected with one <strong>an</strong>o<strong>the</strong>r. I need only refer <strong>to</strong> <strong>the</strong> connection<br />
known <strong>to</strong> exist between connective tissue cells, cartilage<br />
cells, epi<strong>the</strong>lial cells, &c. And not only may <strong>the</strong> cells <strong>of</strong> one<br />
tissue be continuous with one <strong>an</strong>o<strong>the</strong>r, but <strong>the</strong>y may also be<br />
continuous with <strong>the</strong> cells <strong>of</strong> o<strong>the</strong>r tissues. ... It is true<br />
that <strong>the</strong> cells <strong>of</strong> blood <strong>an</strong>d lymph <strong>an</strong>d <strong>the</strong> ripe generative cells<br />
are completely isolated. But <strong>the</strong> former, in <strong>the</strong>ir first stages<br />
<strong>of</strong> growth, form part <strong>of</strong> <strong>the</strong> syncytium, as in all probability do<br />
<strong>the</strong> latter also. This continuity, which for a priori reasons<br />
we should expect, has hi<strong>the</strong>r<strong>to</strong> been regarded as a fact <strong>of</strong> little<br />
morphological import<strong>an</strong>ce <strong>an</strong>d relegated <strong>to</strong> <strong>the</strong> category <strong>of</strong><br />
secondary features. The ovum, it is said, segments in<strong>to</strong><br />
completely isolated cells, <strong>an</strong>d <strong>the</strong> connection between <strong>the</strong>m is<br />
a secondary feature acquired late in development. It has<br />
always been considered that <strong>the</strong> first stage in <strong>the</strong> evolution<br />
<strong>of</strong> <strong>the</strong> Metazoa was a colonial Pro<strong>to</strong>zoon, i. e. a mass <strong>of</strong> perfectly<br />
isolated unicellular org<strong>an</strong>isms, derived by complete division<br />
from a single cell. Now while I do not wish <strong>to</strong> exalt <strong>the</strong> facts<br />
<strong>of</strong> <strong>the</strong> cleavage <strong>an</strong>d early development <strong>of</strong> Peripatus <strong>to</strong> a position<br />
<strong>of</strong> undue import<strong>an</strong>ce, or <strong>to</strong> maintain that <strong>of</strong> <strong>the</strong>mselves<br />
<strong>the</strong>y are sufficient <strong>to</strong> destroy this conception <strong>of</strong> <strong>the</strong> origin <strong>an</strong>d
140 GILBERT 0. BOUENB.<br />
structure <strong>of</strong> a Metazoon, I think I am justified in pointing<br />
out that, if <strong>the</strong>y are found <strong>to</strong> be <strong>of</strong> general application, our<br />
ideas on <strong>the</strong>se subjects trill have <strong>to</strong> undergo considerable<br />
modification. The <strong>an</strong>cestral metazoon will no longer be<br />
looked upon as a colonial pro<strong>to</strong>zoon, but ra<strong>the</strong>r as having<br />
<strong>the</strong> nature <strong>of</strong> a multinucleated infusori<strong>an</strong>, with a mouth<br />
leading in<strong>to</strong> a central vacuolated tract <strong>of</strong> pro<strong>to</strong>plasm. The<br />
continuity between <strong>the</strong> various cells <strong>of</strong> <strong>the</strong> adult—<strong>the</strong> connections<br />
between <strong>the</strong> nerves <strong>an</strong>d muscles und sensory epi<strong>the</strong>lium,<br />
receive <strong>an</strong> adequate morphological expl<strong>an</strong>ation, <strong>being</strong> due <strong>to</strong><br />
a primitive continuity which has never been broken. In<br />
short, if <strong>the</strong>se facts are generally applicable, development c<strong>an</strong><br />
no longer be looked upon as <strong>being</strong> essentially <strong>the</strong> formation <strong>of</strong><br />
a number <strong>of</strong> units from a single primitive unit, <strong>an</strong>d <strong>the</strong><br />
co-ordination <strong>an</strong>d modification <strong>of</strong> <strong>the</strong>se units in<strong>to</strong> a harmonious<br />
whole. But it must ra<strong>the</strong>r be regarded as a multiplication <strong>of</strong><br />
nuclei <strong>an</strong>d a specialisation <strong>of</strong> tracts <strong>an</strong>d vacuoles in a continuous<br />
mass <strong>of</strong> vacuolated pro<strong>to</strong>plasm."<br />
This is a temperate <strong>an</strong>d lucid statement <strong>of</strong> a suggestion<br />
which is still worthy <strong>of</strong> serious consideration, <strong>the</strong> more so<br />
since it had been shown, but a short time previous, that<br />
pro<strong>to</strong>plasmic continuity between <strong>the</strong> tissue-cells <strong>of</strong> pl<strong>an</strong>ts is <strong>of</strong><br />
very general occurrence, if not <strong>the</strong> rule. And, as a his<strong>to</strong>rical<br />
fact, <strong>the</strong> continuity <strong>of</strong> pro<strong>to</strong>plasm was a phenomenon familiar<br />
<strong>to</strong> <strong>an</strong>imal his<strong>to</strong>logists long before it was proved for vegetable<br />
tissues; indeed <strong>the</strong>re were authors who, before <strong>Mr</strong>. Walter<br />
Gardiner's researches were published, were disposed <strong>to</strong> regard<br />
pro<strong>to</strong>plasmic continuity as a characteristic <strong>of</strong> <strong>an</strong>imal org<strong>an</strong>isation,<br />
discontinuity as a characteristic <strong>of</strong> vegetable org<strong>an</strong>isation.<br />
I have quoted at length because <strong>Mr</strong>. Sedgwick from <strong>being</strong><br />
temperate has become intemperate, <strong>an</strong>d from <strong>being</strong> lucid he<br />
has become obscure; so that, were I <strong>to</strong> deal only with his<br />
latest utter<strong>an</strong>ces, I should be quite at a loss <strong>to</strong> know what his<br />
maturer views might be.<br />
What follows, <strong>the</strong>n, may be taken <strong>to</strong> be a not unfair statement<br />
<strong>of</strong> his position. That from <strong>the</strong> connection known <strong>to</strong>
A CRITICISM OP THE OELL-THEOKY. . 141<br />
exist between some cells composing adult tissues, <strong>the</strong>re is <strong>an</strong><br />
<strong>an</strong>tecedent probability that similar connections exist between<br />
all cells composing all tissues; <strong>an</strong>d this probability is heightened<br />
by observations made on <strong>the</strong> development <strong>of</strong> Peripatus, by <strong>the</strong><br />
fact that <strong>the</strong> so-called mesenchyme cells in Avi<strong>an</strong> <strong>an</strong>d Selachi<strong>an</strong><br />
embryos are continuous, <strong>an</strong>d not isolated, as was once supposed,<br />
<strong>an</strong>d by a study <strong>of</strong> <strong>the</strong> developing nerves <strong>of</strong> Elasmobr<strong>an</strong>chs.<br />
And that it follows from this that <strong>the</strong> morphological concept<br />
<strong>of</strong> a cell, so far from <strong>being</strong> <strong>of</strong> primary, is al<strong>to</strong>ge<strong>the</strong>r <strong>of</strong> Secondary<br />
import<strong>an</strong>ce, <strong>an</strong>d that progress in <strong>the</strong> knowledge <strong>of</strong><br />
structure is impossible so long as men persistently regard<br />
cells as <strong>the</strong> fundamental structural units on which <strong>the</strong> phenomena<br />
m<strong>an</strong>ifested by org<strong>an</strong>ised <strong>being</strong>s depend. The true<br />
method <strong>of</strong> enquiry must be a study <strong>of</strong> <strong>the</strong> growth, extension,<br />
vacuolation <strong>an</strong>d specialisation <strong>of</strong> <strong>the</strong> living subst<strong>an</strong>ce—pro<strong>to</strong>plasm.<br />
It is in this sense that I propose <strong>to</strong> deal with <strong>Mr</strong>. <strong>Sedgwick's</strong><br />
views, <strong>an</strong>d he will pardon me if I have misinterpreted <strong>the</strong>m.<br />
At <strong>an</strong>y rate, I have done my best <strong>to</strong> underst<strong>an</strong>d <strong>the</strong>m.<br />
I would wish <strong>to</strong> show, in <strong>the</strong> first place, that <strong>the</strong>re is very<br />
slender ground for <strong>the</strong> accusations which <strong>Mr</strong>. Sedgwick levels,<br />
in <strong>an</strong> unsparing m<strong>an</strong>ner, against his zoological contemporaries.<br />
He goes so far as <strong>to</strong> say that <strong>the</strong>ir eyes are blinded by <strong>the</strong>ory<br />
<strong>to</strong> <strong>the</strong> most patent facts, <strong>an</strong>d that " <strong>the</strong>y are constrained by<br />
this <strong>the</strong>ory,"—<strong>the</strong> cell <strong>the</strong>ory,—" with which <strong>the</strong>ir minds are<br />
saturated, not only <strong>to</strong> see things which do not exist, but<br />
actually <strong>to</strong> figure <strong>the</strong>m." This is abuse <strong>an</strong>d not argument;<br />
if <strong>Mr</strong>. Sedgwick were <strong>to</strong> remember <strong>the</strong> qualifying sentence in<br />
his writings <strong>of</strong> 1886, "if <strong>the</strong>y are <strong>of</strong> general application," he<br />
would recognise that <strong>the</strong>re is little occasion for accusing<br />
Zoologists <strong>of</strong> perversely ignoring <strong>the</strong> views which he <strong>the</strong>n<br />
Set forth.<br />
For, in fact, <strong>the</strong> phenomena <strong>to</strong> which he draws our attention<br />
have received <strong>the</strong>ir due meed <strong>of</strong> recognition from <strong>the</strong> time<br />
that <strong>the</strong> cellular structure <strong>of</strong> tissues was first studied,<br />
More recent researches have enlarged our knowledge <strong>of</strong> pro<strong>to</strong>plasmic<br />
continuity, but it is still a phenomenon far from <strong>being</strong>
142 GILBERT 0. BOURNE.<br />
<strong>of</strong> such universal application as <strong>to</strong> constrain us <strong>to</strong> ab<strong>an</strong>don<br />
that very useful morphological concept—a cell.<br />
For some years past <strong>the</strong> study <strong>of</strong> cells, <strong>of</strong> <strong>the</strong>ir ultimate<br />
structure, <strong>of</strong> <strong>the</strong>ir chemical <strong>an</strong>d physical properties, <strong>of</strong> phenomena<br />
which accomp<strong>an</strong>y <strong>the</strong>ir growth <strong>an</strong>d division, has been<br />
carried on with a minuteness which a short time ago was<br />
undreamt <strong>of</strong>. And attention has been directed, not only <strong>to</strong><br />
<strong>the</strong> cells composing adult tissues, but in <strong>the</strong> most marked<br />
degree <strong>to</strong> <strong>the</strong> successive formation <strong>of</strong> cells from <strong>the</strong> primitive<br />
unit, <strong>the</strong> oosperm, <strong>an</strong>d <strong>to</strong> <strong>the</strong> fate which each subsequently<br />
undergoes in <strong>the</strong> course <strong>of</strong> development. In place <strong>of</strong> <strong>the</strong> <strong>of</strong>fh<strong>an</strong>d<br />
statements <strong>of</strong> older embryologists, that <strong>the</strong> ovum divides<br />
in<strong>to</strong> two, four, eight, sixteen segments, <strong>an</strong>d so forth, we have<br />
<strong>the</strong> most accurate <strong>an</strong>d minute accounts <strong>of</strong> <strong>the</strong> successive<br />
formation <strong>of</strong> cells, <strong>of</strong> <strong>the</strong> place which each occupies in <strong>the</strong><br />
developing embryo, <strong>of</strong> its parentage <strong>an</strong>d <strong>of</strong> its progeny, <strong>an</strong>d<br />
<strong>of</strong> <strong>the</strong> share taken by <strong>the</strong> last named in <strong>the</strong> building up <strong>of</strong> <strong>the</strong><br />
adult tissues. In short, we have a number <strong>of</strong> cell-lineages,<br />
which show that in a number <strong>of</strong> <strong>an</strong>imals, some <strong>of</strong> which are<br />
widely separate from one <strong>an</strong>o<strong>the</strong>r, <strong>the</strong> formation <strong>of</strong> cells from<br />
<strong>the</strong> ovum follows courses which are ei<strong>the</strong>r identical or so<br />
closely similar that <strong>the</strong> differences excite our wonder far leBS<br />
th<strong>an</strong> <strong>the</strong> similarities. So minute are <strong>the</strong>se investigations that<br />
every karyokinetic figure has been followed in every cell, up<br />
<strong>to</strong> a stage where <strong>the</strong>ir number becomes bewildering.<br />
I refer, <strong>of</strong> course, <strong>to</strong> <strong>the</strong> remarkable series <strong>of</strong> observations<br />
which were begun by Selenka, Arnold L<strong>an</strong>g, Hallez, Blochm<strong>an</strong>n,<br />
<strong>an</strong>d o<strong>the</strong>rs, <strong>an</strong>d have been carried <strong>to</strong> <strong>the</strong> highest<br />
perfection by von Wistinghausen, E. B. Wilson, Heymons,<br />
<strong>an</strong>d Lillie.<br />
It would be impossible, in such <strong>an</strong> essay as this, <strong>to</strong> deal<br />
adequately with <strong>the</strong> results obtained by <strong>the</strong>se authors; <strong>an</strong>d it<br />
is unnecessary, since <strong>the</strong>ir works are within reach <strong>of</strong> everyone.<br />
It is enough <strong>to</strong> say here that a perusal <strong>of</strong> <strong>the</strong>m does not tend<br />
<strong>to</strong> diminish <strong>the</strong> import<strong>an</strong>ce which we have been accus<strong>to</strong>med <strong>to</strong><br />
attribute <strong>to</strong> <strong>the</strong> cell in developmental processes.<br />
Nothing c<strong>an</strong> be more clear th<strong>an</strong> <strong>the</strong> fact that, in Nereis or
A CRITICISM OF THE CELL-THEORY. 143<br />
in Unio, <strong>the</strong>re result from <strong>the</strong> division <strong>of</strong> <strong>the</strong> ovum separate<br />
pro<strong>to</strong>plasmic corpuscles, as distinct from one <strong>an</strong>o<strong>the</strong>r as one<br />
room in a house is distinct from <strong>an</strong>o<strong>the</strong>r, each <strong>of</strong> which is not<br />
only separate, but contains within itself definite, <strong>an</strong>d probably<br />
limited, qualities (at least at stages beyond eight or sixteen<br />
cells). One might almost say that, after <strong>the</strong> earliest stages,<br />
each blas<strong>to</strong>mere has a definite task allotted <strong>to</strong> it, which it<br />
faithfully <strong>an</strong>d punctually performs, according <strong>to</strong> a prescribed<br />
course. To each, it might be said in figurative l<strong>an</strong>guage, isgiven<br />
material, which it must place, not <strong>an</strong>ywhere, but in one<br />
particular part <strong>of</strong> <strong>the</strong> edifice.<br />
In considering <strong>the</strong>se very remarkable researches, it is not<br />
sufficient, for <strong>the</strong> present purpose, <strong>to</strong> say that no connection<br />
between <strong>the</strong> blas<strong>to</strong>meres was observed. Such connections<br />
may have existed <strong>an</strong>d have been overlooked; as <strong>the</strong> connections,<br />
which undoubtedly exist, between pl<strong>an</strong>t cells were<br />
for a long time overlooked. But, a priori, such connections<br />
are improbable. For, as has been said, <strong>the</strong> qualities <strong>of</strong> each<br />
blas<strong>to</strong>mere are limited. Each is specialised before <strong>an</strong>y form<br />
ch<strong>an</strong>ges become visible; each plays one part, <strong>an</strong>d one part<br />
Only in tissue formation. If <strong>the</strong>ir pro<strong>to</strong>plasm were continuous,<br />
<strong>being</strong> made so by uniting str<strong>an</strong>ds, <strong>the</strong>n, as <strong>Mr</strong>. Sedgwick has<br />
expressed it, <strong>the</strong> molecular constitution <strong>of</strong> <strong>an</strong>y part would in<br />
time spread through <strong>the</strong> whole mass. But <strong>the</strong> molecular<br />
constitution <strong>of</strong> <strong>the</strong> blas<strong>to</strong>meres must be different, for <strong>the</strong>ir<br />
m<strong>an</strong>ifestations are different, <strong>an</strong>d we may possibly see, in this<br />
case, some expl<strong>an</strong>ation, obscure though it may be, <strong>of</strong> <strong>the</strong> isolation<br />
<strong>of</strong> <strong>the</strong> form elements from one <strong>an</strong>o<strong>the</strong>r.<br />
Fur<strong>the</strong>r th<strong>an</strong> this, <strong>the</strong>re is objective pro<strong>of</strong> that <strong>the</strong> cells<br />
constituting <strong>the</strong> early embryos <strong>of</strong> <strong>the</strong>se forms are separate.<br />
They exhibit remarkable shiftings <strong>of</strong> position, which render<br />
<strong>the</strong> existence <strong>of</strong> connecting str<strong>an</strong>ds <strong>of</strong> pro<strong>to</strong>plasm highly improbable,<br />
<strong>an</strong>d <strong>the</strong> migrations <strong>of</strong> some cells—e. g. those in<br />
Nereis named c 1>5< <strong>an</strong>d d 1>6> by Wilson—are <strong>of</strong> such <strong>an</strong> extent<br />
that, if <strong>the</strong>re were pro<strong>to</strong>plasmic continuity, <strong>the</strong>y would be<br />
impossible.<br />
It is no exaggeration <strong>to</strong> say that this is evidence which-
144 GILBERT 0. BOURNE.<br />
effectually disposes <strong>of</strong> <strong>the</strong> idea that a syncytial <strong>the</strong>ory <strong>of</strong><br />
<strong>an</strong>imal orgaaisation is <strong>of</strong> general application.<br />
It does more th<strong>an</strong> this, it shows that <strong>the</strong>re are not a few<br />
inst<strong>an</strong>ces in which cells possess a morphological <strong>an</strong>d physiological<br />
signific<strong>an</strong>ce greater th<strong>an</strong> was at one time supposed.<br />
There are numerous o<strong>the</strong>r cases in which, at <strong>an</strong> early stage<br />
<strong>of</strong> development, cells w<strong>an</strong>der far from <strong>the</strong> position in which<br />
<strong>the</strong>y originated, <strong>an</strong>d become placed so far from <strong>the</strong> parent<br />
cells from which <strong>the</strong>y sprung, that <strong>an</strong>y idea <strong>of</strong> pro<strong>to</strong>plasmic<br />
continuity is impossible. As examples I may mention: <strong>the</strong><br />
outer layer cells <strong>of</strong> Cornacuspougige <strong>an</strong>d Silicispongise, which, as<br />
Maas has shown, go through remarkable migrations; <strong>the</strong> mesoblast<br />
<strong>of</strong> Calli<strong>an</strong>ira bialata, Beroe <strong>an</strong>d Cydippe, as described<br />
by Metschnik<strong>of</strong>f, whose statements are confirmed by<br />
observations made (but unfortunately not published) by <strong>Mr</strong>.<br />
Riches on Hormiphora plumosa; <strong>the</strong> lower endoderm<br />
cells <strong>of</strong> Discocoelis, Eurylepta, <strong>an</strong>d Lep<strong>to</strong>pl<strong>an</strong>a, as described<br />
by L<strong>an</strong>g, Hallez, <strong>an</strong>d Selenka.<br />
In short, <strong>the</strong> evidence is overwhelming, <strong>an</strong>d it must be<br />
taken <strong>to</strong> be very clearly established that <strong>the</strong>re are numerous<br />
cases in which <strong>the</strong>re is not "a primitive continuity which has<br />
never been broken."<br />
It is apparent, <strong>the</strong>n, that morphologists have been amply<br />
justified in refusing <strong>to</strong> recognise <strong>Mr</strong>. <strong>Sedgwick's</strong> views as <strong>to</strong><br />
<strong>the</strong> syncytial nature <strong>of</strong> <strong>an</strong>imals, <strong>an</strong>d <strong>the</strong>re is no justification<br />
for <strong>the</strong> strong l<strong>an</strong>guage which he uses <strong>to</strong>wards <strong>the</strong>m on<br />
account <strong>of</strong> <strong>the</strong>ir refusal.<br />
It is, on <strong>the</strong> o<strong>the</strong>r h<strong>an</strong>d, quite possible that <strong>the</strong> frequency <strong>of</strong><br />
<strong>the</strong> occurrence <strong>of</strong> pro<strong>to</strong>plasmic continuity between developing<br />
tissue-cells may have been overlooked or ignored by a few<br />
authors, <strong>an</strong>d that those who have done so have been led in<strong>to</strong><br />
<strong>the</strong> error <strong>of</strong> attributing <strong>to</strong>o great <strong>an</strong>d <strong>to</strong>o fundamental import<strong>an</strong>ce<br />
<strong>to</strong> <strong>the</strong> cell as <strong>an</strong> independent vital unit (Lebenseinheit).<br />
But, in point <strong>of</strong> fact, I am unable <strong>to</strong> find, in <strong>the</strong> writings <strong>of</strong><br />
<strong>an</strong>y reputable biologist, <strong>an</strong>y statement <strong>to</strong> <strong>the</strong> effect that <strong>an</strong><br />
org<strong>an</strong>ism is composed <strong>of</strong> independent <strong>an</strong>d isolated units. One<br />
may, it is true, find passages here <strong>an</strong>d <strong>the</strong>re which, when
A CRITICISM OF THE CELL-THEORY. 145<br />
removed from <strong>the</strong> context, might be made <strong>to</strong> bear such <strong>an</strong><br />
interpretation. I have questioned my pupils with regard <strong>to</strong><br />
such passages, <strong>an</strong>d I find that <strong>the</strong>y do in fact put such <strong>an</strong><br />
interpretation upon <strong>the</strong>m. For inst<strong>an</strong>ce, in Waller's ' Introduction<br />
<strong>to</strong> Hum<strong>an</strong> Physiology' <strong>the</strong> following passage occurs<br />
on page 2: " The org<strong>an</strong>ism is a community; its individuals<br />
are cells; groups <strong>of</strong> its individuals are org<strong>an</strong>s." Here we<br />
have <strong>an</strong> example <strong>of</strong> <strong>the</strong> d<strong>an</strong>ger <strong>of</strong> <strong>the</strong> <strong>to</strong>o free use <strong>of</strong> illustrative<br />
l<strong>an</strong>guage. In every illustration <strong>the</strong>re lurks a fallacy. The<br />
fallacy may not have been present <strong>to</strong> <strong>the</strong> mind <strong>of</strong> <strong>the</strong> author;<br />
but if <strong>the</strong> illustration alone is used, without a lucid expl<strong>an</strong>ation<br />
<strong>of</strong> its me<strong>an</strong>ing, <strong>the</strong> fallacy may be <strong>the</strong> one thing which impresses<br />
itself on <strong>the</strong> minds <strong>of</strong> his readers. In this case <strong>the</strong>re<br />
is a fallacy in <strong>the</strong> <strong>an</strong>alogy, so <strong>of</strong>ten made use <strong>of</strong> for purposes <strong>of</strong><br />
popular exposition, between <strong>an</strong> org<strong>an</strong>ism <strong>an</strong>d a community. If<br />
<strong>the</strong> <strong>an</strong>alogy is used without <strong>the</strong> necessary reservations it leads<br />
<strong>to</strong> confusion, for <strong>the</strong> reader is only <strong>to</strong>o prone <strong>to</strong> tr<strong>an</strong>sfer <strong>to</strong><br />
<strong>the</strong> org<strong>an</strong>ic unit <strong>the</strong> idea <strong>of</strong> <strong>the</strong> individual isolated m<strong>an</strong>, who<br />
is <strong>the</strong> social unit. The org<strong>an</strong>ic unit may in some cases be<br />
individual <strong>an</strong>d isolated, but in <strong>the</strong> great majority <strong>of</strong> inst<strong>an</strong>ces<br />
it has lost, wholly or partially, its individuality, <strong>an</strong>d is not<br />
isolated. It becomes a subordinate part <strong>of</strong> a higher individality,<br />
which in its turn may be subordinate <strong>to</strong> <strong>an</strong> individuality <strong>of</strong> a<br />
still higher order. This has been explained in <strong>the</strong> most lucid<br />
<strong>an</strong>d masterly m<strong>an</strong>ner by Hackel, in his ' Allgemeine Ana<strong>to</strong>mie<br />
der Org<strong>an</strong>ismen,' published in 1866; <strong>an</strong>d nobody who has<br />
carefully studied that work c<strong>an</strong> fail <strong>to</strong> have a clear underst<strong>an</strong>ding<br />
<strong>of</strong> <strong>the</strong> subject. Yet it is <strong>to</strong> Hackel that <strong>the</strong> doctrine<br />
<strong>of</strong> a cell-republic is <strong>of</strong>ten attributed ! Clearly by those persons<br />
only who have not read his works. For he insists, over <strong>an</strong>d<br />
over again, upon a distinction (which since <strong>the</strong> researches <strong>of</strong><br />
<strong>Mr</strong>. Walter Gardiner no longer holds good) between <strong>the</strong><br />
org<strong>an</strong>isation <strong>of</strong> pl<strong>an</strong>ts <strong>an</strong>d that <strong>of</strong> <strong>an</strong>imals, namely, that <strong>the</strong><br />
special characteristic <strong>of</strong> pl<strong>an</strong>ts lies in <strong>the</strong> preponder<strong>an</strong>ce <strong>of</strong> <strong>the</strong><br />
perfected <strong>an</strong>d differentiated individuals <strong>of</strong> <strong>the</strong> first order—<strong>the</strong><br />
cells or plastids. "Der wesentliche tec<strong>to</strong>logische Character<br />
der Pfl<strong>an</strong>zen liegt in der vorwiegenden Ausbildung und DifFer-<br />
VOL. 38, PAET 1.—NEW SEE.<br />
K
146 GILBERT 0. BOUBNE.<br />
enzirung der Individuen erster Ordnung, der Plastiden" (op,<br />
cit.j p. 222). Of <strong>an</strong>imals he says, on <strong>the</strong> contrary, " Der<br />
wesentliche tec<strong>to</strong>logische character der Thiere liegt sowohl in<br />
der verwickelteren Zusammensetzung der Thierleibes aus weit<br />
differenzirten Individuen verschiedener Ordnung, als auch<br />
besonders in der verschiedenartigsten Ausbildung der Individuen<br />
zweiter Ordnung, der Org<strong>an</strong>e, welche viel m<strong>an</strong>nichfaltiger,<br />
als bei den Pfl<strong>an</strong>zen und Protisten, differenzirt und<br />
polymorph sind. Die Plastiden, die Individuen erster Ordnung,<br />
sind bei Thieren allermeist Zellen, und zwar meistens Nacktzellen<br />
(ohne Membr<strong>an</strong>) weniger Hautzellen (mit Membr<strong>an</strong>).<br />
Sehr haufig, und allgemein in den entwickelten Personen,<br />
vereinigen sich bei den Thieren mehjere Nacktzellen zur<br />
Bildung von Zells<strong>to</strong>cken (Nervefasern, Muskelfasem), was bei<br />
den Pfl<strong>an</strong>zen nur bei der Bildung der Milchsaftgefasse und<br />
der Spiralgefasse geschiecht. Daher verliert bei den<br />
Thieren stets wenigstens ein Theil Zellen ihre individuelle<br />
Selbst<strong>an</strong>digkeit, wahrend sie dieselbe<br />
in den Pfl<strong>an</strong>zen meist behalten."<br />
The last sentence, which I have put in italics, shows most<br />
clearly that, as long ago as 1866, Hackel did not regard <strong>the</strong><br />
<strong>an</strong>imal org<strong>an</strong>ism as a community, whose individuals are cells;<br />
<strong>an</strong>d it is <strong>the</strong> fact that he applied <strong>the</strong> term " cell-republic " <strong>to</strong><br />
pl<strong>an</strong>ts, intending <strong>the</strong>reby <strong>to</strong> emphasise <strong>the</strong> difference which<br />
he believed <strong>to</strong> exist between vegetable <strong>an</strong>d <strong>an</strong>imal org<strong>an</strong>isation.<br />
So that, as a matter <strong>of</strong> his<strong>to</strong>ry, whilst pl<strong>an</strong>ts used <strong>to</strong> be<br />
considered <strong>to</strong> be colonies <strong>of</strong> independent life units, <strong>an</strong>imals<br />
were not. A certain exch<strong>an</strong>ge <strong>of</strong> opinion seems <strong>to</strong> have taken<br />
place more recently. Some few zoologists <strong>an</strong>d <strong>an</strong>imal physiologists,<br />
borrowing from Hackel <strong>the</strong> term cell-republic, have<br />
thoughtlessly applied it, with all its implications, <strong>to</strong> <strong>an</strong>imal<br />
org<strong>an</strong>isation, whilst bot<strong>an</strong>ists, influenced by <strong>Mr</strong>. Walter Gardiner's<br />
researches, have insisted more <strong>an</strong>d more upon <strong>the</strong><br />
individuality <strong>of</strong> <strong>the</strong> pl<strong>an</strong>t as a whole, <strong>an</strong>d <strong>the</strong> subordination <strong>of</strong><br />
its component parts, <strong>the</strong> cells. None <strong>the</strong> less, <strong>the</strong> facts <strong>of</strong><br />
cell fusion <strong>an</strong>d cell communication have never been wholly<br />
overlooked by zoologists, <strong>an</strong>d recent years have brought <strong>to</strong>
A CRITICISM OP THE CELL-THEORT. 147<br />
light facts, such as <strong>the</strong> continuity <strong>of</strong> cartilage cells, which were<br />
unsuspected when Hackel wrote.<br />
I am <strong>the</strong>refore far from <strong>being</strong> satisfied that <strong>the</strong> independentlife-unit<br />
<strong>the</strong>ory has had such a domin<strong>an</strong>t influence as <strong>Mr</strong>.<br />
Sedgwick would have us believe; <strong>an</strong>d I am quite certain that<br />
<strong>the</strong> picture which he draws <strong>of</strong> <strong>the</strong> teaching given <strong>to</strong> every<br />
student <strong>of</strong> biology is a travesty <strong>of</strong> <strong>the</strong> truth.<br />
Biology includes bot<strong>an</strong>y as well as zoology, <strong>an</strong>d if we were<br />
<strong>to</strong> allow (which I do not) that zoologists generally have<br />
become as narrow in <strong>the</strong>ir conceptions <strong>of</strong> <strong>the</strong> processes <strong>of</strong><br />
development as <strong>Mr</strong>. Sedgwick says, it is quite certain that<br />
bot<strong>an</strong>ists have not. And as all students <strong>of</strong> biology are—or if<br />
<strong>the</strong>y are not, <strong>the</strong>y ought <strong>to</strong> be—put through a course <strong>of</strong><br />
elementary bot<strong>an</strong>y as well as <strong>of</strong> zoology (in m<strong>an</strong>y schools <strong>the</strong><br />
subjects are combined), grave blame must be imputed <strong>to</strong> those<br />
teachers who have, in <strong>the</strong> later stages <strong>of</strong> <strong>the</strong>ir education,<br />
Warped <strong>the</strong> liberal conceptions which <strong>the</strong>y must have formed<br />
on <strong>the</strong> subject <strong>of</strong> org<strong>an</strong>ic growth <strong>an</strong>d development. For I take<br />
it that, after a study <strong>of</strong> Mucor, Vaucheria, <strong>an</strong>d <strong>the</strong> Myxomycetes,<br />
<strong>the</strong>re is no student so dull but he will have imbibed<br />
ideas respecting cell growth which impel him <strong>to</strong> ask <strong>the</strong><br />
question which as <strong>Mr</strong>. Sedgwick says it is so difficult <strong>to</strong> find<br />
<strong>an</strong>. <strong>an</strong>swer <strong>to</strong>—" What, after all, is a cell?" If, when he asks<br />
this question, he is <strong>to</strong>ld that <strong>the</strong> cell is <strong>an</strong> isolated corpuscle<br />
<strong>of</strong> pro<strong>to</strong>plasm, <strong>the</strong> unit <strong>of</strong> vitality, <strong>an</strong>d that <strong>the</strong>re is " a most<br />
fundamental distinction" between unicellular <strong>an</strong>d multicellular<br />
org<strong>an</strong>isms, <strong>an</strong>d so forth, <strong>the</strong> student may go on his way<br />
rejoicing, for that he has at last been given a clear <strong>an</strong>d t<strong>an</strong>gible<br />
statement; but none <strong>the</strong> less he will have been started on a<br />
very wrong path. I have not a widespread experience <strong>of</strong><br />
zoological teaching, but I know, at least, that Pr<strong>of</strong>essor<br />
Laokester's pupils are not started on that path. The truth is,<br />
<strong>an</strong>d, if I am not much mistaken, zoologists <strong>an</strong>d bot<strong>an</strong>ists alike<br />
have long been possessed <strong>of</strong> it, that <strong>the</strong>re is no fundamental<br />
but only a formal distinction between unicellular <strong>an</strong>d multicellular<br />
org<strong>an</strong>isms; that <strong>the</strong> cell is a form concept founded<br />
on a very wide basis <strong>of</strong> experience, whereby we c<strong>an</strong> conveniently
148 GILBERT 0. BOURNE.<br />
interpret <strong>to</strong> our minds one <strong>of</strong> <strong>the</strong> most universal <strong>of</strong> org<strong>an</strong>ic<br />
phenomena, viz. <strong>the</strong> splitting up <strong>of</strong> pro<strong>to</strong>plasmic masses during<br />
growth in<strong>to</strong> a number <strong>of</strong> more or less distinct corpuscles.<br />
It will not be out <strong>of</strong> place if I quote here a passage from<br />
von Sach's 'Vorlesungen iiber Pfl<strong>an</strong>zenphysiologie 5 (English<br />
edition, tr<strong>an</strong>slated by H. Marshall Ward, 1887, p. 73). "To<br />
m<strong>an</strong>y <strong>the</strong> cell is always <strong>an</strong> independent living <strong>being</strong>, which<br />
sometimes exists for itself alone, <strong>an</strong>d sometimes becomes<br />
'joined with o<strong>the</strong>rs'—millions <strong>of</strong> its like, in order <strong>to</strong> form a<br />
cell colony, or as Hackel has named it for <strong>the</strong> pl<strong>an</strong>t particularly,<br />
a cell republic. To o<strong>the</strong>rs again, <strong>to</strong> whom <strong>the</strong> author<br />
<strong>of</strong> this book also belongs, cell-formation is a phenomenon very<br />
general, it is true, in org<strong>an</strong>ic life, but still only <strong>of</strong> secondary<br />
signific<strong>an</strong>ce; at all events it is merely one <strong>of</strong> <strong>the</strong> numerous<br />
expressions <strong>of</strong> <strong>the</strong> formative forces which reside in all matter,<br />
in <strong>the</strong> highest degree, however, in org<strong>an</strong>ic subst<strong>an</strong>ce."<br />
That this is a great limitation <strong>of</strong> <strong>the</strong> cell <strong>the</strong>ory, both as<br />
propounded by its authors <strong>an</strong>d as held by m<strong>an</strong>y zoologists, is<br />
not <strong>to</strong> be denied; <strong>an</strong>d <strong>Mr</strong>. Sedgwick might well be content<br />
if some such statement were made <strong>the</strong> established doctrine<br />
as regards cells. It appears <strong>to</strong> me that some such limited<br />
statement is necessary if we are <strong>to</strong> have <strong>an</strong>y proposition<br />
universally applicable <strong>to</strong> org<strong>an</strong>ic structure; but with this<br />
reservation, that I c<strong>an</strong>not regard as <strong>of</strong> secondary signific<strong>an</strong>ce<br />
that which all experience shows <strong>to</strong> be <strong>the</strong> expression par<br />
excellence <strong>of</strong> org<strong>an</strong>ic growth.<br />
In admitting this much, a large part <strong>of</strong> <strong>Mr</strong>. <strong>Sedgwick's</strong><br />
dem<strong>an</strong>d is conceded, for it is not <strong>to</strong> be denied that <strong>the</strong> cell<br />
<strong>the</strong>ory has been very differently <strong>an</strong>d much more dogmatically<br />
stated by quite recent authors.<br />
We have, for inst<strong>an</strong>ce, Dr. Oscar Hertwig's recent work,<br />
' Die Zelle und die Gewebe.' He begins dogmatically enough<br />
by saying, "Thiere und Pfl<strong>an</strong>zen, so verschiedenartig in ihren<br />
ausseren Erscheinung, stimmen in den Grundlagen ihres <strong>an</strong>a<strong>to</strong>mischen<br />
Aufbaues iiberein; denn beide sind aus gleichartigen,<br />
meist nur mikroskopisch wahrnehmbaren Elementareinheiten<br />
zusammengesetzt. . . . Denn die Zellen, in
A CRITICISM OF THE CELL-THEORY. 149<br />
welche der Ana<strong>to</strong>m die pfl<strong>an</strong>zlichen und thierischen Org<strong>an</strong>ismen<br />
zerlegt, sind die Trager der Lebensfunctionen, sie sind,<br />
wie Virchow sich ausgedriickt hat die 'Lebenseinheiten.'<br />
Von diesem Gesichtspunkt aus betrachtet, erscheint der<br />
Gesammtlebensprocess eines zusammengesetzten Org<strong>an</strong>ismus<br />
nichts Anderes zu sein als das hochst verwickelte Resultat<br />
der einzelnen Lebensprocesse seiner zahlreichen, verschieden<br />
functionirenden Zellen." The whole book is written "von<br />
diesem Gesichtspunkt aus," <strong>an</strong>d, admirable as it is, <strong>the</strong>re is<br />
reason <strong>to</strong> think that its value is somewhat impaired by <strong>the</strong><br />
excessive value attributed <strong>to</strong> <strong>the</strong> cell as <strong>an</strong> independent vital<br />
unit.<br />
In passing, I may remark that this passage <strong>of</strong> 0. Hertwig's<br />
gives a very precise <strong>an</strong>d definite statement <strong>of</strong> <strong>the</strong> cell <strong>the</strong>ory,<br />
as it is held now, by a very great authority; <strong>an</strong>d a reference<br />
<strong>to</strong> older works would have shown <strong>Mr</strong>. Sedgwick that, so stated,<br />
it is practically <strong>the</strong> same as what its authors stated. 1<br />
For <strong>the</strong> original words <strong>of</strong> Schw<strong>an</strong>n are <strong>the</strong>se: " The elementary<br />
parts <strong>of</strong> all tissues are formed <strong>of</strong> cells in <strong>an</strong> <strong>an</strong>alogous<br />
though very diversified m<strong>an</strong>ner, so that it may be asserted<br />
that <strong>the</strong>re is one universal principle <strong>of</strong> development for <strong>the</strong><br />
elementary parts <strong>of</strong> org<strong>an</strong>isms, however different, <strong>an</strong>d that<br />
this principle is <strong>the</strong> formation <strong>of</strong> cells In inferior<br />
pl<strong>an</strong>ts <strong>an</strong>y given cell may be separated from <strong>the</strong> pl<strong>an</strong>t <strong>an</strong>d c<strong>an</strong><br />
grow alone. So that here are whole pl<strong>an</strong>ts consisting <strong>of</strong> cells<br />
which c<strong>an</strong> be positively proved <strong>to</strong> have independent vitality.<br />
Now, as all cells grow according <strong>to</strong> <strong>the</strong> same laws, <strong>an</strong>d consequently<br />
<strong>the</strong> cause <strong>of</strong> growth c<strong>an</strong>not in one case lie in <strong>the</strong> cell<br />
<strong>an</strong>d in <strong>an</strong>o<strong>the</strong>r in <strong>the</strong> whole org<strong>an</strong>ism, <strong>an</strong>d since it may be<br />
fur<strong>the</strong>r proved that some cells, which do not differ from <strong>the</strong><br />
rest in <strong>the</strong>ir mode <strong>of</strong> growth, are developed independently,<br />
we must ascribe <strong>to</strong> all cells <strong>an</strong> independent vitality; that is<br />
such combinations <strong>of</strong> molecules as occur in <strong>an</strong>y single cell are<br />
capable <strong>of</strong> setting free <strong>the</strong> power by which it is enabled <strong>to</strong><br />
take up fresh molecules. The cause <strong>of</strong> nutrition <strong>an</strong>d growth<br />
1 ''lam not concerned with what its authors held."—<strong>Mr</strong>. Sedgwick, op. cit.,<br />
p. 88.
150 GILBERT 0. BOUBNE.<br />
resides, not in <strong>the</strong> org<strong>an</strong>ism as a whole, but in <strong>the</strong> separate<br />
elementary parts, <strong>the</strong> cells."<br />
The definitions <strong>of</strong> Hertwig are a re-statement in o<strong>the</strong>r words<br />
<strong>of</strong> <strong>the</strong> salient features <strong>of</strong> <strong>the</strong> <strong>the</strong>ory <strong>of</strong> Schw<strong>an</strong>n, <strong>an</strong>d it is <strong>an</strong><br />
error <strong>to</strong> speak <strong>of</strong> <strong>an</strong> unsubst<strong>an</strong>tial cell ph<strong>an</strong><strong>to</strong>m. Nor is <strong>the</strong>re<br />
<strong>an</strong>y unsubst<strong>an</strong>tiality about <strong>the</strong> cellular <strong>the</strong>ory <strong>of</strong> development,<br />
which, I may remind my readers, originated with Eemak.<br />
The cellular <strong>the</strong>ory <strong>of</strong> development, taking as its starting point<br />
<strong>the</strong> conclusions <strong>of</strong> Schleiden <strong>an</strong>d Schw<strong>an</strong>n that all org<strong>an</strong>isms<br />
are cells or composed <strong>of</strong> <strong>an</strong> aggregate <strong>of</strong> cells, states that<br />
every cell is formed by <strong>the</strong> division <strong>of</strong> a pre-existing cell, not<br />
as Schw<strong>an</strong>n had supposed, by differentiation within a structureless<br />
cy<strong>to</strong>blastema. 1 Hence Virchow's well-known aphorism,<br />
" omnis cellula e cellule," which, besides denying abiogenesis,<br />
expresses <strong>the</strong> cellular <strong>the</strong>ory <strong>of</strong> development as succintly as<br />
possible.<br />
It would have been a great adv<strong>an</strong>tage <strong>to</strong> his own argument,<br />
<strong>an</strong>d also <strong>to</strong> his critic, if <strong>Mr</strong>. Sedgwick had given <strong>the</strong> clear <strong>an</strong>d<br />
authoritative expositions <strong>of</strong> <strong>the</strong> cellular <strong>the</strong>ory which lay ready<br />
<strong>to</strong> haud, instead <strong>of</strong> confusing <strong>the</strong> issue by a whimsical account<br />
<strong>of</strong> his experience <strong>of</strong> morphological teaching.<br />
Let us now examine <strong>the</strong> cell-<strong>the</strong>ory, as stated by Hertwig,<br />
in <strong>the</strong> light <strong>of</strong> our present knowledge <strong>of</strong> <strong>an</strong>imal <strong>an</strong>d vegetable<br />
structure.<br />
It would not be a difficult task <strong>to</strong> demonstrate <strong>the</strong> general<br />
truth <strong>of</strong> Virchow's aphorism. Wherever <strong>the</strong>re is a cell, it may<br />
be shown <strong>to</strong> be <strong>the</strong> product, <strong>an</strong>d generally <strong>the</strong> immediate<br />
product, <strong>of</strong> a pre-existing cell. But it would seem that some<br />
biologists have added <strong>an</strong> unwarr<strong>an</strong>table corollary <strong>to</strong> Virchow's<br />
generalisation, <strong>an</strong>d would say, " Nil nisi cellula e cellula."<br />
Now from a certain aspect this might be considered true;<br />
everything depends on <strong>the</strong> question as <strong>to</strong> what is a cell?<br />
Hertwig has pointed out, with much truth, that our present<br />
conception <strong>of</strong> a cell is inseparably connected with our<br />
conception <strong>of</strong> pro<strong>to</strong>plasm. We are still very far from under-<br />
1 <strong>Mr</strong>. Sedgwick appears <strong>to</strong> have le<strong>an</strong>ings <strong>to</strong>wards a cy<strong>to</strong>blastema, as I<br />
shall show fur<strong>the</strong>r on.
A CRITICISM OF THE CELL-THEORY. 151<br />
st<strong>an</strong>ding <strong>the</strong> structure <strong>of</strong> pro<strong>to</strong>plasm, <strong>an</strong>d it might be said<br />
that, if we know nothing <strong>of</strong> <strong>the</strong> component, it is useless <strong>to</strong><br />
make assertions about <strong>the</strong> compost; but it will at least be<br />
useful <strong>to</strong> criticise <strong>the</strong> attempts which have been made.<br />
Hertwig gives this definition, which is <strong>the</strong> same as that<br />
originally given by Max Schulze. A cell is a corpuscle <strong>of</strong><br />
pro<strong>to</strong>plasm in which is contained a specially org<strong>an</strong>ised constituent,<br />
<strong>the</strong> nucleus. (Die Zelle ist ein kliitnpchen von Pro<strong>to</strong>plasma,<br />
das in seinen Innern einen besonders geformten<br />
Best<strong>an</strong>d<strong>the</strong>il, den Kern (Nucleus) einschliesst.) This at first<br />
sight seems satisfac<strong>to</strong>ry enough, but <strong>the</strong> more one examines<br />
it, <strong>the</strong> less satisfac<strong>to</strong>ry does it appear, in view <strong>of</strong> <strong>the</strong> different<br />
kinds <strong>of</strong> org<strong>an</strong>isms which are usually described as single cells.<br />
If a corpuscle containing a nucleus is a cell, is a corpuscle<br />
Containing two or more nuclei also a cell ? And still more, is<br />
a large mass <strong>of</strong> pro<strong>to</strong>plasm containing m<strong>an</strong>y nuclei <strong>to</strong> be<br />
regarded as a cell ? Such a mass, I me<strong>an</strong>, as Botrydium,<br />
Caulerpa, or Codium, or even Pelomyxa. By m<strong>an</strong>y authors<br />
<strong>the</strong>se org<strong>an</strong>isms are regarded as single multinucleate cells, but<br />
I am far from <strong>being</strong> convinced that this is a right view <strong>of</strong> <strong>the</strong><br />
case. 1<br />
If <strong>the</strong>re is one thing more th<strong>an</strong> <strong>an</strong>o<strong>the</strong>r which has come<br />
in<strong>to</strong> prominence as <strong>the</strong> result <strong>of</strong> recent research, both bot<strong>an</strong>ical<br />
<strong>an</strong>d zoological, it is <strong>the</strong> fundamental import<strong>an</strong>ce <strong>of</strong> <strong>the</strong><br />
nucleus <strong>to</strong> cell life. So m<strong>an</strong>y minute org<strong>an</strong>isms, which at one<br />
1 With regard <strong>to</strong> <strong>the</strong> argument which follows, I would remind my readers<br />
that Hackel, thirty years ago, clearly expressed <strong>the</strong> view which I am now<br />
urging (see his " Allgemeine Ana<strong>to</strong>mie den Org<strong>an</strong>ismen," forming <strong>the</strong> first<br />
part <strong>of</strong> <strong>the</strong> ' Generelle Morphologie,' p. 296). " Es muss hierbei ausdriicklich<br />
errinert werden, dass wir unter eine Zelle nur einen Plasma-Klumpen mit<br />
einem Kerne verstehen konnen. Der haufig gebrauchte Ausdruck einer<br />
' mehrkernigen Zelle' ist eine Contradictio in adjec<strong>to</strong>, da ja eben nur die<br />
Einheit des Kerns die individuelle Einheit der Zelle als eines Elementar-<br />
Org<strong>an</strong>ismus bedingt. Jeder Plasmaklumpen, der mehr als einen Kern<br />
umschliessfc, moge er nun von einer Membr<strong>an</strong> umhiillt sein oder nicht, ist eine<br />
Vielheit von Zellen, und wenn diese Yielheit eine bestimmte einheitliche<br />
Form besitzt, so haben wir sie als Zellens<strong>to</strong>ck zu dem R<strong>an</strong>ge eines Org<strong>an</strong>es<br />
erster Ordnung zu erheben." This view, however, has been controverted by<br />
m<strong>an</strong>y authorities, as will appear fur<strong>the</strong>r on.
152 GILBERT 0. BOURNE.<br />
time were believed <strong>to</strong> be non-nucleate, have since been shown<br />
<strong>to</strong> contain nuclei, or at <strong>an</strong>y rate nuclear matter, that we are<br />
<strong>to</strong>lerably well justified in saying that <strong>the</strong> nucleus, or its<br />
equivalent, is <strong>an</strong> essential constituent <strong>of</strong> <strong>the</strong> cell. At all<br />
events we know that division <strong>of</strong> <strong>the</strong> nuclear subst<strong>an</strong>ce, whe<strong>the</strong>r<br />
mi<strong>to</strong>tic or ami<strong>to</strong>tic, is all-import<strong>an</strong>t as a prelude <strong>to</strong> <strong>an</strong>d<br />
accomp<strong>an</strong>iment <strong>of</strong> cell division. The experiments <strong>of</strong> Gruber<br />
<strong>an</strong>d Verworn show that if Amoebae are artificially divided, <strong>the</strong><br />
parts cut <strong>of</strong>f will regenerate <strong>an</strong>d lead <strong>an</strong> independent existence<br />
if <strong>the</strong>y contain nuclear matter, but if <strong>the</strong>y do not, <strong>the</strong>y soon<br />
perish. Fragmentation <strong>of</strong> <strong>the</strong> nucleus—by which is produced<br />
a so-called multinucleate condition, <strong>of</strong>ten <strong>of</strong> considerable<br />
duration—is a prelude <strong>to</strong> spore formation, i. e. <strong>to</strong> <strong>the</strong><br />
division <strong>of</strong> <strong>the</strong> cell in<strong>to</strong> m<strong>an</strong>y parts. Mi<strong>to</strong>tic division is highly<br />
characteristic <strong>of</strong> division <strong>of</strong> <strong>the</strong> cell in<strong>to</strong> two parts. It is very<br />
difficult <strong>to</strong> draw distinctions, but it is worth consideration<br />
whe<strong>the</strong>r <strong>the</strong> temporary multinucleate condition ending in<br />
multiple fission, which is common in pro<strong>to</strong>zoa, has not a<br />
different value <strong>to</strong> <strong>the</strong> perm<strong>an</strong>ently multinucleate condition <strong>of</strong><br />
some pl<strong>an</strong>ts <strong>an</strong>d <strong>an</strong>imals, which are generally called unicellular.<br />
In <strong>the</strong> one case(e. g.Podophrya,Thalassicolla,Actinosph8erium)<br />
division or fragmentation <strong>of</strong> <strong>the</strong> nucleus leads, sooner or later,<br />
<strong>to</strong> <strong>the</strong> separation <strong>of</strong> cells, each containing a fragment <strong>of</strong> <strong>the</strong><br />
original nucleus. In <strong>the</strong> Coeloblastse (Siphonese, e. g. Caulerpa)<br />
<strong>the</strong> repeated division <strong>of</strong> <strong>the</strong> nucleus is not followed by <strong>an</strong>y<br />
cell division, but <strong>the</strong> org<strong>an</strong>ism is throughout life a mass <strong>of</strong><br />
continuous undivided pro<strong>to</strong>plasm. The pl<strong>an</strong>t, as von Sachs<br />
says, is <strong>of</strong> considerable size, develops roots, even leaf-forming<br />
shoots, <strong>an</strong>d in its pro<strong>to</strong>plasm hundreds <strong>an</strong>d thous<strong>an</strong>ds <strong>of</strong> cell<br />
nuclei are contained, which with adv<strong>an</strong>cing growth are multiplied<br />
by division, <strong>an</strong>d obtain a definite arr<strong>an</strong>gement within <strong>the</strong><br />
pro<strong>to</strong>plasm. And, as in <strong>the</strong> case in cellular pl<strong>an</strong>ts, <strong>the</strong> nuclei<br />
are specially aggregated at <strong>the</strong> growing points. The whole<br />
behaviour is just that <strong>of</strong> a multicellular pl<strong>an</strong>t, but <strong>the</strong>re are no<br />
partition walls.<br />
It is stretching <strong>the</strong> point very far <strong>to</strong> call this a single cell.<br />
And, in fact, it is <strong>an</strong> inconsistency <strong>to</strong> do so, for where, by <strong>an</strong>
A CRITICISM OF THE CELL-THEORY. 153<br />
essentially similar process, a continuous sheet <strong>of</strong> pro<strong>to</strong>plasm<br />
containing m<strong>an</strong>y nuclei is formed as a tissue-constituent <strong>of</strong> a<br />
multicellular <strong>an</strong>imal or pl<strong>an</strong>t, we do not call <strong>the</strong> whole multinuclear<br />
tract a single cell—we call it a syncytium, or take<br />
some roundabout way <strong>of</strong> describing it. Such a case is <strong>the</strong><br />
formation <strong>of</strong> <strong>the</strong> endosperm in <strong>the</strong> embryo-sac <strong>of</strong> Ph<strong>an</strong>erogams.<br />
By repeated mi<strong>to</strong>tic division <strong>of</strong> <strong>the</strong> nucleus <strong>an</strong>d growth<br />
<strong>of</strong> <strong>the</strong> surrounding cy<strong>to</strong>plasm, a tract <strong>of</strong> continuous pro<strong>to</strong>plasm<br />
is formed, containing m<strong>an</strong>y nuclei. At a later stage<br />
partitions are formed <strong>an</strong>d <strong>the</strong> mass is divided up in<strong>to</strong> cells, but<br />
for a period <strong>the</strong> endosperm has a structure which recalls that<br />
<strong>of</strong> <strong>the</strong> Coeloblastse. C<strong>an</strong> we say that <strong>the</strong> condition in <strong>the</strong><br />
endosperm is <strong>to</strong> be regarded as multicellular because it is not<br />
perm<strong>an</strong>ent, <strong>an</strong>d that <strong>the</strong> condition in <strong>the</strong> Coeloblastse is <strong>to</strong> be<br />
regarded as unicellular because it is perm<strong>an</strong>ent ? If this is<br />
allowed <strong>the</strong> consequences are far-reaching, for it follows that<br />
<strong>the</strong> multinuclear phase in Actinosphserium <strong>an</strong>d o<strong>the</strong>r Pro<strong>to</strong>zoa<br />
is also multicellular, because not perm<strong>an</strong>ent.<br />
Take, again, <strong>the</strong> case <strong>of</strong> <strong>the</strong> Myce<strong>to</strong>zoa. The plasmodium <strong>of</strong><br />
Badharaia or Fuligo is not unicellular, for it is formed by <strong>the</strong><br />
union <strong>of</strong> m<strong>an</strong>y cells: it is not called multicellular, because<br />
<strong>the</strong>re are no cell divisions : yet we draw, rightly enough, a<br />
distinction between <strong>the</strong> plasmodium, where cell bodies fuse but<br />
<strong>the</strong> nuclei do not unite, <strong>an</strong>d <strong>the</strong> single cell resulting from, conjugation,<br />
where <strong>the</strong> nuclei do unite.<br />
A survey <strong>of</strong> <strong>the</strong> facts must lead <strong>to</strong> <strong>the</strong> conclusion that <strong>the</strong>re<br />
is <strong>an</strong> intermediate phase between <strong>the</strong> unicellular <strong>an</strong>d <strong>the</strong> multicellular<br />
condition, which is <strong>the</strong> multinucleate but non-cellular<br />
condition, 1 <strong>an</strong>d that <strong>the</strong>re is no fundamental distinction<br />
1 The term non-cellular does not exactly represent <strong>the</strong> condition which it<br />
is intended <strong>to</strong> describe. Yet, if one adheres <strong>to</strong> existing nomenclature, it is<br />
difficult <strong>to</strong> find a substitute. The term "cell," though founded on <strong>an</strong><br />
erroneous conception, is so firmly established in biological l<strong>an</strong>guage that it<br />
would probably be impossible <strong>to</strong> eject it. Yet if one were <strong>to</strong> make general<br />
use <strong>of</strong> <strong>the</strong> Greek equivalent KVTIS (literally a little box), which has already<br />
come in<strong>to</strong> such favour as <strong>to</strong> have respectable claims on our attention, ons<br />
might adopt much more exact expressions. Thus <strong>the</strong> uninucleate Pro<strong>to</strong>zoa<br />
might be said <strong>to</strong> exhibit a monocjtial condition, multicellular org<strong>an</strong>isms a
154 GILBERT 0. BOURNE.<br />
between Pro<strong>to</strong>zoa as unicellular, <strong>an</strong>d Metazoa as multicellular<br />
org<strong>an</strong>isms. I should hardly have thought it worth while <strong>to</strong><br />
insist upon this had not <strong>Mr</strong>. Sedgwick written "that <strong>an</strong><br />
org<strong>an</strong>ism may consist <strong>of</strong> one cell or <strong>of</strong> several cells in association<br />
with one <strong>an</strong>o<strong>the</strong>r. We draw <strong>the</strong> most fundamental distinction<br />
between <strong>the</strong> two kinds <strong>of</strong> org<strong>an</strong>ism, <strong>an</strong>d we divide <strong>the</strong><br />
<strong>an</strong>imal kingdom in<strong>to</strong> two great groups <strong>to</strong> receive <strong>the</strong>m. As a<br />
pro<strong>of</strong> <strong>of</strong> <strong>the</strong> import<strong>an</strong>ce which we attach <strong>to</strong> this feature <strong>of</strong><br />
org<strong>an</strong>isation we assert that a m<strong>an</strong> is nearer, morphologically,<br />
<strong>to</strong> a tapeworm th<strong>an</strong> a tapeworm is <strong>to</strong> a paramcecium."<br />
Bot<strong>an</strong>ists, who have <strong>the</strong> great adv<strong>an</strong>tage <strong>of</strong> studying <strong>the</strong><br />
physiology concurrently with <strong>the</strong> morphology <strong>of</strong> <strong>the</strong>ir subject,<br />
make no fundamental division in<strong>to</strong> Pro<strong>to</strong>phyta <strong>an</strong>d Metaphyta.<br />
For <strong>the</strong>m, unicellular pl<strong>an</strong>ts, hypopolycytial pl<strong>an</strong>ts, Fungi <strong>an</strong>d<br />
Algae are alike Thallophyta, <strong>an</strong>d a passage from Goebel may<br />
serve <strong>to</strong> illustrate <strong>the</strong> point <strong>of</strong> view which leads <strong>the</strong>m <strong>to</strong> classify<br />
<strong>to</strong>ge<strong>the</strong>r org<strong>an</strong>isms which, from <strong>the</strong> point <strong>of</strong> view <strong>of</strong> "independent<br />
life units," would appear widely separate. "From<br />
this initial stage "—a single small cell—" <strong>the</strong> process <strong>of</strong> development<br />
may adv<strong>an</strong>ce, yet still within <strong>the</strong> limits <strong>of</strong> a single<br />
cell, <strong>an</strong>d whilst <strong>the</strong> cell increases in size, <strong>of</strong>ten reaching<br />
dimensions without parallel in <strong>the</strong> vegetable kingdom, ei<strong>the</strong>r<br />
<strong>the</strong> differentiation <strong>of</strong> <strong>the</strong> cell-contents or that <strong>of</strong> <strong>the</strong> external<br />
form, as shown by <strong>the</strong> br<strong>an</strong>ching, may make most rapid progress.<br />
In o<strong>the</strong>r cases <strong>the</strong> .growth <strong>of</strong> <strong>the</strong> cells is accomp<strong>an</strong>ied<br />
by cell-division, <strong>the</strong> thallus becoming multicellular, <strong>an</strong>d <strong>the</strong><br />
single cell producing, according <strong>to</strong> <strong>the</strong> nature <strong>of</strong> <strong>the</strong> pl<strong>an</strong>t,<br />
a cell row, or a cellular filament, a cell surface or simple tissue<br />
layer, or lastly a cell mass increasing in every direction.'"<br />
polycy tial condition, <strong>an</strong>d tbe so-called non-cellular condition <strong>of</strong> Cceloblastse<br />
<strong>an</strong>d Opalina might appropriately be called hypopolycytial, <strong>the</strong> preposition<br />
v7ro <strong>being</strong> used in a modifying sense, as expressing <strong>the</strong> intermediate stage<br />
between one <strong>an</strong>d m<strong>an</strong>y. The term syncytial, which is now used in a loose<br />
sense, is strictly applicable <strong>to</strong> <strong>the</strong> early condition <strong>of</strong> <strong>the</strong> plasmodia <strong>of</strong> <strong>the</strong><br />
Myxomycetes, which are formed by <strong>the</strong> fusion <strong>of</strong> m<strong>an</strong>y units in a monocytial<br />
condition, <strong>an</strong>d are <strong>the</strong>refore different from org<strong>an</strong>isms which exhibit a hypopolycytial<br />
condition. In later stages <strong>the</strong> nuclei <strong>of</strong> <strong>the</strong> plasmodia multiply by<br />
division; thus <strong>the</strong> hypopolycytial is added <strong>to</strong> <strong>the</strong> syncytial condition.
A CRITICISM OP THE CELL-THEORY. 155<br />
Although in this passage, which is descriptive <strong>of</strong> Thallophytes,<br />
Goebel attaches <strong>to</strong>o much import<strong>an</strong>ce, as I think, <strong>to</strong> <strong>the</strong> continuity<br />
<strong>of</strong> a vesicle as determining <strong>the</strong> unicellularity <strong>of</strong> a pl<strong>an</strong>t,<br />
he shows clearly enough that he regards <strong>the</strong> growth <strong>an</strong>d mode<br />
<strong>of</strong> extension <strong>of</strong> <strong>the</strong> pro<strong>to</strong>plasm, not its division in<strong>to</strong> cells, as<br />
<strong>the</strong> feature <strong>of</strong> fundamental import<strong>an</strong>ce.<br />
There is <strong>the</strong> fur<strong>the</strong>r property in pl<strong>an</strong>ts that continuity<br />
between <strong>the</strong> cells <strong>of</strong> highly org<strong>an</strong>ised multicellular pl<strong>an</strong>ts has<br />
been shown <strong>to</strong> be <strong>of</strong> very general, if not universal, occurrence.<br />
And if complete separation were <strong>to</strong> be insisted upon as a<br />
characteristic <strong>of</strong> a cell, <strong>an</strong>y given Angiosperm, or o<strong>the</strong>r highly<br />
org<strong>an</strong>ised pl<strong>an</strong>t, could no longer be considered as <strong>an</strong> aggregate<br />
<strong>of</strong> life units, but ra<strong>the</strong>r as a conjunct mass <strong>of</strong> pro<strong>to</strong>plasm,<br />
imperfectly broken up in<strong>to</strong> corpuscles, in each <strong>of</strong> which <strong>the</strong>re<br />
is a nucleus. It is but a step from <strong>the</strong> much-br<strong>an</strong>ched, multinucleate<br />
Coeloblastse, which have no partitions, <strong>to</strong> <strong>the</strong> forma,<br />
tion <strong>of</strong> incomplete partitions, breaking up <strong>the</strong> pro<strong>to</strong>plasm in<strong>to</strong><br />
small masses, which remain, however, linked with one <strong>an</strong>o<strong>the</strong>r,<br />
<strong>an</strong>d so preserve <strong>an</strong> original continuity similar <strong>to</strong> that <strong>of</strong> <strong>the</strong><br />
Coeloblastse, which has only apparently but never actually been<br />
broken.<br />
So much has this idea impressed itself on <strong>the</strong> minds <strong>of</strong> some<br />
observers, that H<strong>of</strong>meister suggested that <strong>the</strong> creeping motion<br />
<strong>of</strong> <strong>the</strong> plasmodia <strong>of</strong> <strong>the</strong> Myxomycetes <strong>an</strong>d <strong>the</strong>ir later tr<strong>an</strong>sfer,<br />
mation in<strong>to</strong> fructification, is representative <strong>of</strong> <strong>the</strong> simplest type<br />
<strong>of</strong> growth, even for more highly org<strong>an</strong>ised pl<strong>an</strong>ts. This<br />
opinion has been quoted with approval by von Sachs, who,<br />
before even <strong>the</strong> continuity <strong>of</strong> <strong>the</strong> pro<strong>to</strong>plasm <strong>of</strong> pl<strong>an</strong>t cells<br />
was established, wrote that " fundamentally every pl<strong>an</strong>t, how-*<br />
ever highly org<strong>an</strong>ised, is a pro<strong>to</strong>plasmic body, coherent in<br />
itself, which, clo<strong>the</strong>d without by a cell-wall <strong>an</strong>d traversed<br />
internally by innumerable partitions, grows; <strong>an</strong>d it appears<br />
that <strong>the</strong> more vigorously this formation <strong>of</strong> chambers <strong>an</strong>d<br />
walls proceeds with <strong>the</strong> nutrition <strong>of</strong> <strong>the</strong> pro<strong>to</strong>plasm, <strong>the</strong> higher<br />
also is <strong>the</strong> development attained by <strong>the</strong> <strong>to</strong>tal org<strong>an</strong>isation."<br />
Expressed in this way, <strong>the</strong> phenomenon <strong>of</strong> cell-formation is<br />
represented <strong>to</strong> us as <strong>being</strong> nothing more th<strong>an</strong> a particular
156 GILBERT 0. BOURNE.<br />
m<strong>an</strong>ifestation <strong>of</strong> growth, <strong>an</strong>d <strong>Mr</strong>. Sedgwick may contend that<br />
his views are <strong>the</strong>reby conceded, <strong>an</strong>d that <strong>the</strong> <strong>an</strong>cestral metazoon<br />
may, on this aspect, be considered as " a multinucleate<br />
infusori<strong>an</strong> with a month leading in<strong>to</strong> a central vacuolated mass<br />
<strong>of</strong> pro<strong>to</strong>plasm." There may be truth in <strong>the</strong> contention, yet<br />
none <strong>the</strong> less we may hold fast <strong>to</strong> <strong>the</strong> concept <strong>of</strong> a cell, as I shall<br />
attempt <strong>to</strong> show fur<strong>the</strong>r on. And it may be observed in passing<br />
that <strong>Mr</strong>. Walter Gardiner, in describing <strong>an</strong>d emphasising<br />
<strong>the</strong> continuity <strong>of</strong> pro<strong>to</strong>plasm in pl<strong>an</strong>ts, expressly stated " that<br />
<strong>the</strong> presence <strong>of</strong> minute perforations <strong>of</strong> <strong>the</strong> cell-wall need not<br />
lead <strong>to</strong> <strong>an</strong>y modification <strong>of</strong> our general ideas as <strong>to</strong> <strong>the</strong> mech<strong>an</strong>ism<br />
<strong>of</strong> <strong>the</strong> cell," a proposition which most reflective persons<br />
will be cordially inclined <strong>to</strong> agree with. For this much is<br />
certain, that <strong>the</strong> formation <strong>of</strong> cells is not merely <strong>the</strong> expression<br />
<strong>of</strong> one out <strong>of</strong> m<strong>an</strong>y formative processes which reside in org<strong>an</strong>ic<br />
matter, but is <strong>the</strong> formative process, par excellence, which<br />
obtains both in <strong>an</strong>imal <strong>an</strong>d vegetable tissues.<br />
Thus far I have endeavoured <strong>to</strong> show that <strong>the</strong> independentlife-unit<br />
<strong>the</strong>ory has not held <strong>the</strong> minds <strong>of</strong> zoologists in <strong>an</strong> iron<br />
bondage, much less <strong>the</strong> minds <strong>of</strong> biologists, for, when reference<br />
is made <strong>to</strong> biologists, bot<strong>an</strong>ists must be taken in<strong>to</strong> equal<br />
account with zoologists.<br />
It is, however, arguable that, whatever bot<strong>an</strong>ists have thought,<br />
zoologists have not followed <strong>the</strong>ir example, but have publicly<br />
maintained a complete adherence <strong>to</strong> <strong>the</strong> independent-life-unit<br />
<strong>the</strong>ory in its most limited form, whatever reservations <strong>the</strong>y<br />
may privately have made in <strong>the</strong>ir own minds.<br />
But it may be doubted whe<strong>the</strong>r <strong>the</strong> argument holds good.<br />
1 have already shown that passages which seem <strong>to</strong> state most<br />
dogmatically that cells are separate individuals, prove on<br />
examination <strong>to</strong> be nothing more th<strong>an</strong> illustrations ; <strong>an</strong>d it is<br />
<strong>to</strong> be.remembered that ideas founded on bot<strong>an</strong>ical evidence<br />
must always be reflected on <strong>the</strong> minds <strong>of</strong> zoologists, <strong>an</strong>d one<br />
may certainly say that conceptions <strong>of</strong> <strong>an</strong>imal structure have<br />
<strong>of</strong> late years been considerably modified by <strong>the</strong> light thrown<br />
upon org<strong>an</strong>ic structure in general by bot<strong>an</strong>ical investigation.<br />
Some zoologists may possibly have given <strong>to</strong>o little attention, <strong>to</strong>
A CRITICISM OP THE CELL-THEORY. 157<br />
growth without division in<strong>to</strong> cells, because <strong>the</strong>re are not in<br />
<strong>the</strong> <strong>an</strong>imal kingdom <strong>an</strong>y such striking inst<strong>an</strong>ces <strong>of</strong> massive<br />
growth without cell division as are exhibited by <strong>the</strong> Coeloblastse,<br />
especially if we leave out <strong>of</strong> consideration <strong>the</strong> Myce<strong>to</strong>zoa, as<br />
belonging <strong>to</strong> <strong>the</strong> debateable terri<strong>to</strong>ry between <strong>the</strong> two kingdoms.<br />
Never<strong>the</strong>less, we have inst<strong>an</strong>ces <strong>of</strong> growth <strong>an</strong>d mi<strong>to</strong>tic nuclear<br />
division, unaccomp<strong>an</strong>ied by cell division, which are not apparently<br />
a mere prelude <strong>to</strong> division. Take <strong>the</strong> single inst<strong>an</strong>ce<br />
<strong>of</strong> Opalina r<strong>an</strong>arum. Because this org<strong>an</strong>ism is microscopic,<br />
<strong>an</strong>d may be described, without <strong>of</strong>fence <strong>to</strong> our sense <strong>of</strong> proportion,<br />
as a corpuscle, it is invariably called unicellular. Yet in<br />
essential features it resembles one <strong>of</strong> <strong>the</strong> Coeloblastee. It<br />
contains numerous nuclei, which divide mi<strong>to</strong>tically, <strong>an</strong>d <strong>the</strong>ir<br />
division is <strong>an</strong> accomp<strong>an</strong>iment <strong>of</strong> <strong>the</strong> growth <strong>of</strong> <strong>the</strong> mature<br />
org<strong>an</strong>ism. Themultinucleate mature condition is <strong>of</strong> considerable<br />
duration. In <strong>the</strong> reproductive process this multinucleate<br />
corpuscle divides repeatedly, until a number <strong>of</strong> small <strong>of</strong>fspring<br />
are formed, each containing several, usually four or five, nuclei.<br />
The minute product <strong>of</strong> fission <strong>the</strong>n encysts, <strong>an</strong>d it is remarkable<br />
that ei<strong>the</strong>r during or immediately after encystment <strong>the</strong> several<br />
nuclei break up, <strong>an</strong>d a single new nucleus is formed,—presumably<br />
it is constituted out <strong>of</strong> <strong>the</strong> chromatin <strong>of</strong> <strong>the</strong> several<br />
nuclei. The form which emerges from <strong>the</strong> cyst grows, <strong>an</strong>d<br />
growth is accomp<strong>an</strong>ied by repeated mi<strong>to</strong>tic division <strong>of</strong> <strong>the</strong><br />
nucleus till <strong>the</strong> mature condition is reached. The whole<br />
his<strong>to</strong>ry reminds one <strong>of</strong> that <strong>of</strong> a Myce<strong>to</strong>zoon, except that <strong>the</strong><br />
young do not fuse <strong>to</strong> form a plasmodium, but simply grow up;<br />
in this respect Opalina resembles <strong>the</strong> Coeloblastae, differing from<br />
<strong>the</strong>m, however, in <strong>the</strong> fact that <strong>the</strong> whole org<strong>an</strong>ism is concerned<br />
in reproduction, not a special part. Although it has, as he<br />
remarks, a distinct "development," Zeller, who first followed<br />
its life his<strong>to</strong>ry, has no doubt that Opalina is a single cell.<br />
Now <strong>the</strong> multinucleate condition is far from uncommon in<br />
<strong>the</strong> Pro<strong>to</strong>zoa, <strong>an</strong>d it may almost be said <strong>to</strong> be <strong>the</strong> rule in <strong>the</strong><br />
Ciliata, if we regard macrouucleus <strong>an</strong>d micronucleus as two<br />
separate nuclei. But putting aside this phenomenon, <strong>the</strong><br />
signific<strong>an</strong>ce <strong>of</strong> which we do not yet clearly underst<strong>an</strong>d, <strong>the</strong>re
158 GILBERT 0. BOURNE.<br />
are several Ciliata which have as m<strong>an</strong>y as one hundred nuclei,<br />
e.g. Holophrya oblonga, Lagynus elongatus, <strong>an</strong>d<br />
Uroleptus roacovi<strong>an</strong>us. 1 I do not include as multinuclear<br />
thoseformsinwhich,asiuTrachelocerca phoeni copter us or<br />
Chcenia teres, <strong>the</strong> chromatin is scattered throughout<strong>the</strong>pro<strong>to</strong>plasm<br />
in <strong>the</strong> form <strong>of</strong> minute gr<strong>an</strong>ules. Those Pro<strong>to</strong>zoa only may<br />
be considered multinucleate in which <strong>the</strong>re are several welldefined<br />
aggregations <strong>of</strong> chromatin. And even if <strong>the</strong> Ciliata<br />
above mentioned may not be considered truly multinucleate, but<br />
<strong>to</strong> possess onlya fragmented nucleus,<strong>the</strong>re c<strong>an</strong> be no doubtabout<br />
some Amoebae, e.g. Amoeba quarta <strong>an</strong>d o<strong>the</strong>rs described by<br />
Gruber. 2 In <strong>the</strong> last-named <strong>the</strong> multinuclear state is const<strong>an</strong>t<br />
; as Gruber says, " es sich nicht etwa urn vorubergehende<br />
Entwicklungszust<strong>an</strong>de h<strong>an</strong>delt." He watched <strong>the</strong>se Amoebae<br />
for a long period, expecting that <strong>the</strong> large number <strong>of</strong> nuclei<br />
would at last find its expl<strong>an</strong>ation in reproduction by multiple<br />
fission, but he was unable <strong>to</strong> observe <strong>an</strong>y such culmination.<br />
Dr. Gruber is a great authority, <strong>an</strong>d he, equally with Zeller<br />
<strong>an</strong>d o<strong>the</strong>rs, is quite positive that <strong>the</strong> multinuclear Pro<strong>to</strong>zoa<br />
are truly unicellular. His reasons are, that closely allied<br />
species are uninuclear, <strong>an</strong>d that <strong>the</strong> pro<strong>to</strong>plasmic body is continuous—contained<br />
in <strong>the</strong> case <strong>of</strong> Ciliata by a single cuticular<br />
coat. But even he admits that <strong>the</strong> only reasonable interpretation<br />
<strong>of</strong> <strong>the</strong> multinuclear condition is that it is a prelude <strong>to</strong><br />
reproduction, that is, <strong>to</strong> cell division. 3 It is, <strong>the</strong>refore, a condition<br />
intermediate between <strong>the</strong> unicellular <strong>an</strong>d <strong>the</strong> multicellular<br />
condition, or, as I should like <strong>to</strong> call it, a hypopolycytial<br />
condition, <strong>an</strong>d nothing more need be affirmed <strong>of</strong> it.<br />
Zeller is quite precise as <strong>to</strong> his reasons for regarding<br />
Opalina as unicellular. " Die kleinsten. Thierchen aller bek<strong>an</strong>nten<br />
Opalinen, so wie sie von Neuem sich zu entwickeln<br />
beginnen, besitzen nur einen einfachen Kern und entsprechen<br />
1 Maupas, "Etudes des Infusoires cilies," 'Arch. Zool. exper. et gen.' (2),<br />
i, 1883.<br />
2 ' Zeit. fur wiss. Zool.,' xli, p. 186.<br />
' Aug. Gruber, "Ueber vielkernige Pro<strong>to</strong>zoa," 'Biol. Centralblatt,' iv,<br />
p. 710.
A CRITICISM OP THE CELL-THEORY. 159<br />
unzweifelhaft, wie Engelm<strong>an</strong>n schon fiir die von ihm untersuchte<br />
Art nachgeweisen hat,' morphologischvollst<strong>an</strong>digeinereinzigen<br />
Zelle.' Aber auch mit der weiteren Entwicklung <strong>an</strong>dert sich<br />
dar<strong>an</strong> nichts. Mag die Zellhaut zu einer aus vielen einzeln<br />
zerlegbaren B<strong>an</strong>dern bestehenden muskuloses Hiille werden<br />
und mag der Kern in zwei Kerne zerfallen, wie in O. similis<br />
und O. caudata, oder durch fortgestzte Theilungen eine<br />
schliesslich sehr grosse Menge von Kernen aus sich hervorgehen<br />
lassen, wie in O. r<strong>an</strong>arum, 0. obtrigona und 0. dimidiata,<br />
die pro<strong>to</strong>plasmische Korpersubst<strong>an</strong>z selbst zeigt<br />
keine weitere Ver<strong>an</strong>derung als die der Masseuzunahme<br />
und blebt, wie auch Engelm<strong>an</strong>n hervorhebt,<br />
' Zeitlebens eine einzige zusammenh<strong>an</strong>gender Masse,<br />
•wie von eine einzigen Zelle. 5 " I have put <strong>the</strong> last passage<br />
in italics, because it expresses most clearly why Zeller <strong>an</strong>d o<strong>the</strong>r<br />
authors regard multinucleate forms as unicellular, namely<br />
because <strong>the</strong> pro<strong>to</strong>plasm showa no o<strong>the</strong>r ch<strong>an</strong>ge th<strong>an</strong> increase<br />
in size, <strong>an</strong>d because it remains, its life long, a single continuous<br />
mass. The same argument leads m<strong>an</strong>y <strong>to</strong> regard <strong>the</strong><br />
Coeloblastae as unicellular. The continuity <strong>of</strong> <strong>the</strong> pro<strong>to</strong>plasm,<br />
<strong>the</strong>n, is <strong>the</strong> test <strong>of</strong> unicellularity.<br />
If <strong>an</strong>ybody accepts this, he c<strong>an</strong>not escape from its logical<br />
consequences. Not only are multinucleate Pro<strong>to</strong>zoa <strong>an</strong>d<br />
Coeloblastae unicellular, but also <strong>the</strong> whole kingdom <strong>of</strong> pl<strong>an</strong>ts,<br />
for <strong>the</strong>ir pro<strong>to</strong>plasm is continuous: <strong>the</strong> developing Peripatus<br />
is unicellular, for its pro<strong>to</strong>plasm is continuous ; <strong>the</strong> epi<strong>the</strong>lial<br />
cells <strong>of</strong> m<strong>an</strong>y <strong>an</strong>imals, as Max Schulze, Pfitzner, Klein,<br />
Paulicki, Th. Cohn, <strong>an</strong>d o<strong>the</strong>rs have shown, are united by fine<br />
pro<strong>to</strong>plasmic processes much as are <strong>the</strong> cells <strong>of</strong> pl<strong>an</strong>ts, <strong>the</strong>refore<br />
<strong>the</strong> epi<strong>the</strong>lia are unicellular, for <strong>the</strong>ir pro<strong>to</strong>plasm is continuous.<br />
The same may be said for muscle cells (Werner <strong>an</strong>d<br />
Klecki), for connective tissue, for bone cells, for <strong>the</strong> developing<br />
mesoblast <strong>of</strong> Vertebrata (teste Sedgwick, Asshe<strong>to</strong>n, <strong>an</strong>d<br />
o<strong>the</strong>rs), for <strong>the</strong> mesoblast (mesenchyme) <strong>of</strong> trochospheres <strong>an</strong>d<br />
Mollusc<strong>an</strong> larvae (see particularly von Erl<strong>an</strong>ger), <strong>an</strong>d for m<strong>an</strong>y<br />
o<strong>the</strong>r tissues.<br />
Thus <strong>the</strong> inevitable result <strong>of</strong> <strong>an</strong> argument which is me<strong>an</strong>t
160 GILBERT 0. BOURNE.<br />
by those who use it <strong>to</strong> tighten <strong>the</strong> bonds <strong>of</strong> <strong>the</strong> cell-<strong>the</strong>ory is.<br />
<strong>to</strong> loosen <strong>the</strong>m al<strong>to</strong>ge<strong>the</strong>r, <strong>an</strong>d <strong>to</strong> h<strong>an</strong>d us over unbound <strong>to</strong><br />
<strong>Mr</strong>. Sedgwick, who would fetter us once more with a new<br />
doctrine, viz. <strong>the</strong>re is no cell, all org<strong>an</strong>isation is a specialisation<br />
<strong>of</strong> tracts <strong>an</strong>d vacuoles in a continuous mass <strong>of</strong> vacuolated pro<strong>to</strong>plasm.<br />
We do not w<strong>an</strong>t <strong>to</strong> be bound, at least I do not, <strong>an</strong>d if we are<br />
<strong>to</strong> be free we must take refuge in some such lax but comprehensive<br />
statement as that <strong>of</strong> von Sachs, viz. that cell formation<br />
is a phenomenon very general in org<strong>an</strong>ic life ; but even if<br />
we must regard it as only <strong>of</strong> secondary signific<strong>an</strong>ce, it is <strong>the</strong><br />
characteristic expression <strong>of</strong> <strong>the</strong> formative forces which reside<br />
in org<strong>an</strong>ic subst<strong>an</strong>ce.<br />
Now this statement affirms <strong>the</strong> existence <strong>of</strong> cells, <strong>an</strong>d it is<br />
necessary <strong>to</strong> arrive at some underst<strong>an</strong>ding as <strong>to</strong> what is a cell;<br />
what properties are connoted by this term ?<br />
It has become abund<strong>an</strong>tly evident in <strong>the</strong> course <strong>of</strong> this<br />
argument, that whatever o<strong>the</strong>r attributes may be affirmed <strong>of</strong><br />
<strong>the</strong> cell, <strong>the</strong> possession <strong>of</strong> a nucleus is one <strong>of</strong> <strong>the</strong> most import<strong>an</strong>t.<br />
It is impossible <strong>to</strong> disagree with Pfitzner when he<br />
writes, "Wenn wir aber den Kern iiberall und zwar immer<br />
und in alien Stadien als durchaus selbstiindiges Gebilde finden,<br />
so ergiebt sich deraus dass er fur das Bestehen der Zelle<br />
als solchen ein Org<strong>an</strong> von wiel fundamentaler Bedeutung ist<br />
als wir bisher geneigt werden <strong>an</strong>zunehmen." This is also <strong>the</strong><br />
view <strong>of</strong> 0. Hertwig, <strong>an</strong>d it is no new one, for Max Schulze<br />
insisted upon it, <strong>an</strong>d Hackel wrote in 1866, "Ein Plasmaklumpen<br />
ohne Kern ist keine Zelle mehr."<br />
But c<strong>an</strong> we follow Pfitzner when he goes fur<strong>the</strong>r <strong>an</strong>d says,<br />
" bei einer so ausserordentlich Konst<strong>an</strong>z in der g<strong>an</strong>ze Reihe<br />
der Thierformeu, von den Pro<strong>to</strong>zoen bis zu dem Menschen,<br />
k<strong>an</strong>n ich nicht umhin auzunehmen dass iiberhaupt die g<strong>an</strong>ze<br />
Existenz eine Zelle als biologische Einheit <strong>an</strong> das Vorh<strong>an</strong>dsein<br />
eines centralen Korpers, von komplicirten inneren Bau,<br />
gebunden ist, dass also die Chromatinstrukturen nicht etwas<br />
sekundaren erworbenes, sondern die Grrundbediugung vitaler<br />
Existenz der Zelle darstellen. Uud weiter folge ich hieraus
A CRITICISM OF THE CELL-THEORY. 161<br />
das der als Karyokinese bezeichnete Vorg<strong>an</strong>g nicht ein specielle<br />
Kern<strong>the</strong>ilungsmodus, sondern der Kern<strong>the</strong>ilungsmodus<br />
tear' E^o^/jv ist " ?<br />
I think not. Particles <strong>of</strong> chromatin scattered through <strong>the</strong><br />
pro<strong>to</strong>plasm do not constitute a nucleus <strong>an</strong>y more th<strong>an</strong> a heap<br />
<strong>of</strong> bricks constitutes a house. Under such a view, Ciliata like<br />
Trachelocerca phsenicopterus <strong>an</strong>d Chaenia teres would<br />
not be cells, for <strong>the</strong>y have no central nucleus <strong>of</strong> complex structure,<br />
nor have Oscillaria <strong>an</strong>d Bacterium, in which chromatin<br />
gr<strong>an</strong>ules have been discovered. Though <strong>the</strong> case <strong>of</strong> Holosticha<br />
scutellum, in which scattered nuclei (chromatin particles)<br />
unite <strong>an</strong>d fuse <strong>to</strong> form a single central body or nucleus<br />
previous <strong>to</strong> division, may help <strong>to</strong> clear our ideas, it is evident<br />
that <strong>the</strong> dem<strong>an</strong>d for a central org<strong>an</strong>ised constituent is<br />
more th<strong>an</strong> <strong>the</strong> cell conception c<strong>an</strong> bear, especially if <strong>the</strong><br />
dem<strong>an</strong>d carries with it a fur<strong>the</strong>r dem<strong>an</strong>d for <strong>the</strong> universality<br />
<strong>of</strong> mi<strong>to</strong>tic division in nuclei.<br />
In short, before we could accept Hertwig's definition <strong>of</strong><br />
a cell, we should have <strong>to</strong> ask <strong>an</strong>d <strong>an</strong>swer <strong>the</strong> question, What<br />
is a nucleus?<br />
Here I may s<strong>to</strong>p <strong>to</strong> ask whe<strong>the</strong>r it is worth while <strong>to</strong> discuss<br />
<strong>the</strong> grounds <strong>of</strong> a definition which, when made, could not be<br />
acceptable <strong>to</strong> <strong>the</strong> mind <strong>of</strong> everyone. An argument about<br />
definitions would soon l<strong>an</strong>d one in <strong>the</strong> regions <strong>of</strong> scholasticism,<br />
<strong>an</strong>d I have no desire <strong>to</strong> enter in<strong>to</strong> subtleties which would tax<br />
<strong>the</strong> powers <strong>of</strong> a Duns Scotus. To give <strong>an</strong> <strong>an</strong>swer which shall<br />
be beyond all cavil <strong>to</strong> <strong>the</strong> question, What is a nucleus ? would<br />
be about as easy as <strong>to</strong> <strong>an</strong>swer how m<strong>an</strong>y <strong>an</strong>gels c<strong>an</strong> d<strong>an</strong>ce on<br />
<strong>the</strong> point <strong>of</strong> a needle.<br />
The truth is that it is <strong>the</strong> attempt <strong>to</strong> frame short concise<br />
definitions, applicable without exception <strong>to</strong> whole classes <strong>of</strong><br />
phenomena, which leads <strong>to</strong> trouble. The concepts <strong>of</strong> biology<br />
may <strong>an</strong>d should correspond with <strong>the</strong> phenomena we observe,<br />
but <strong>the</strong>y c<strong>an</strong> very seldom be made in<strong>to</strong> universal propositions.<br />
There is no place in <strong>the</strong> science for definitions as exact <strong>an</strong>d<br />
universal as those <strong>of</strong> geometry. The qualities <strong>of</strong> a nucleus are<br />
not <strong>to</strong> be defined like those <strong>of</strong> a point or a line. Such propo-<br />
VOL. 38, PART 1. NEW SERIES. L
162 GILBERT 0. BOURNE.<br />
sitions as we may make are but resting-places for our minds<br />
as we ascend <strong>the</strong> mazy scale <strong>of</strong> org<strong>an</strong>isation. To attempt <strong>to</strong><br />
form definitions, <strong>to</strong> predicate <strong>the</strong> precise attributes <strong>of</strong> whole<br />
classes <strong>of</strong> phenomena, is <strong>to</strong> run counter <strong>to</strong> <strong>the</strong> very genius <strong>of</strong><br />
<strong>the</strong> subject. For what do we me<strong>an</strong> by evolution if not that<br />
life is labile, never resting, prote<strong>an</strong> in its variety? And how<br />
c<strong>an</strong> we express this but in <strong>an</strong> incomplete way, contenting ourselves<br />
with particulars, <strong>an</strong>d trying <strong>to</strong> show that <strong>the</strong> stream,<br />
though it flows in m<strong>an</strong>y <strong>to</strong>rtuous ch<strong>an</strong>nels, is one stream<br />
never<strong>the</strong>less.<br />
<strong>Cell</strong>s <strong>an</strong>d nuclei are prote<strong>an</strong> in <strong>the</strong>ir variety, <strong>an</strong>d since we<br />
very rightly insist on objective study as a preliminary <strong>to</strong> <strong>the</strong><br />
underst<strong>an</strong>ding <strong>of</strong> <strong>the</strong>m, it is not wonderful that <strong>the</strong>y should<br />
give rise <strong>to</strong> this concept in <strong>the</strong> mind <strong>of</strong> one m<strong>an</strong>, <strong>an</strong>d <strong>to</strong> that<br />
concept in <strong>the</strong> mind <strong>of</strong> <strong>an</strong>o<strong>the</strong>r m<strong>an</strong>, <strong>an</strong>d thus it is not surprising<br />
that <strong>the</strong> <strong>the</strong>ory <strong>of</strong> cells should be incapable <strong>of</strong> <strong>being</strong><br />
stated, as <strong>Mr</strong>. Sedgwick complains, "in so m<strong>an</strong>y words in a<br />
m<strong>an</strong>ner satisfac<strong>to</strong>ry <strong>to</strong> everyone."<br />
It is fairly obvious that <strong>Mr</strong>. <strong>Sedgwick's</strong> quarrel with <strong>the</strong><br />
cell-<strong>the</strong>ory beg<strong>an</strong> with <strong>the</strong> dissatisfaction which he felt when<br />
he discovered that doctrines, which he believed <strong>to</strong> be <strong>of</strong> universal<br />
application, were in fact contradicted by several inst<strong>an</strong>ces.<br />
But he fell out <strong>of</strong> Scylla in<strong>to</strong> Charybdis when he supposed<br />
that he could reply <strong>to</strong> a uuiversal affirmative by a universal<br />
negative.<br />
There is <strong>an</strong> old <strong>an</strong>d respectable rule <strong>of</strong> logic that <strong>of</strong> two<br />
contrary propositions both c<strong>an</strong>not be true <strong>an</strong>d both may be<br />
false, whilst <strong>of</strong> two subcontrary propositions both may be<br />
true but both c<strong>an</strong>not be false. Had <strong>Mr</strong>. Sedgwick remembered<br />
this, he would not have attempted <strong>to</strong> overthrow <strong>the</strong><br />
cell-<strong>the</strong>ory by <strong>the</strong> statement <strong>of</strong> a contrary proposition <strong>of</strong><br />
equally universal import.<br />
The cellular <strong>the</strong>ory <strong>of</strong> development in <strong>the</strong> popular form in<br />
which it is <strong>of</strong>ten presented may be briefly summed up somewhat<br />
as follows. The multicellular org<strong>an</strong>ism is a colony, consisting<br />
<strong>of</strong> <strong>an</strong> aggregation <strong>of</strong> separate elementary parts, viz.<br />
cells. The cells are independent life units, <strong>an</strong>d <strong>the</strong> org<strong>an</strong>ism
A CRITICISM OF THE CELL-THEORY. 163<br />
subsists in its parts <strong>an</strong>d in <strong>the</strong> harmonious interaction <strong>of</strong> those<br />
parts.<br />
The falsity <strong>of</strong> this summary is evident when we consider<br />
<strong>the</strong> known facts <strong>of</strong> vegetable org<strong>an</strong>isation; <strong>the</strong> development<br />
<strong>of</strong> Peripatus; <strong>the</strong> union, by me<strong>an</strong>s <strong>of</strong> pro<strong>to</strong>plasmic processes,<br />
<strong>of</strong> epi<strong>the</strong>lial, muscular, <strong>an</strong>d connective-tissue cells; <strong>the</strong> evidence<br />
lately adduced as <strong>to</strong> <strong>the</strong> continuity <strong>of</strong> <strong>the</strong> mesoblast in Elasmobr<strong>an</strong>chs,<br />
Aves <strong>an</strong>d Mammalia, <strong>an</strong>d o<strong>the</strong>r well-known inst<strong>an</strong>ces.<br />
The absolute contrary, as expressed by <strong>Mr</strong>. Sedgwick, is<br />
equally false, viz. that <strong>the</strong> metazoon is a continuous mass <strong>of</strong><br />
nucleated vascular pro<strong>to</strong>plasm, subsisting in <strong>the</strong> unity <strong>of</strong> its<br />
mass. For, as I have shown in <strong>the</strong> earlier part <strong>of</strong> this essay,<br />
<strong>the</strong>re are unequivocal inst<strong>an</strong>ces <strong>of</strong> distinct isolated cells<br />
occurring in <strong>the</strong> embryos <strong>of</strong> m<strong>an</strong>y Metazoa (Nereis, Unio,<br />
Umbrella, Lep<strong>to</strong>pl<strong>an</strong>a). Moreover I am convinced, by my own<br />
studies on <strong>the</strong> his<strong>to</strong>logy <strong>of</strong> Coelenterates, that, whilst <strong>the</strong>re is<br />
org<strong>an</strong>ic connection between m<strong>an</strong>y <strong>of</strong> <strong>the</strong> tissue-cells composing<br />
<strong>the</strong>se org<strong>an</strong>isms, as was demonstrated long ago by <strong>the</strong> bro<strong>the</strong>rs<br />
Hertwig, <strong>the</strong>re are m<strong>an</strong>y o<strong>the</strong>r cells <strong>of</strong> which such continuity<br />
c<strong>an</strong>not be affirmed.<br />
To deal clearly with <strong>the</strong> cell-<strong>the</strong>ory, or ra<strong>the</strong>r with <strong>the</strong> independent-life-unit<br />
<strong>the</strong>ory which has grown out <strong>of</strong> it, we must<br />
split it up in<strong>to</strong> as m<strong>an</strong>y separate propositions as it contains.<br />
These are:<br />
The multicellular org<strong>an</strong>ism is <strong>an</strong> aggregate <strong>of</strong> elementary<br />
parts, viz. cells.<br />
The elementary parts are independent life units.<br />
The harmonious interaction <strong>of</strong> <strong>the</strong> independent life units<br />
constitutes <strong>the</strong> org<strong>an</strong>ism.<br />
Therefore <strong>the</strong> multicellular org<strong>an</strong>ism is a colony (cellrepublic<br />
according <strong>to</strong> Hiickel).<br />
It is not necessary <strong>to</strong> follow <strong>the</strong> <strong>the</strong>ory fur<strong>the</strong>r in<strong>to</strong> <strong>the</strong><br />
consequences which are deducible from <strong>the</strong>se propositions,<br />
e. g. that development consists in <strong>the</strong> separation <strong>of</strong> numerous<br />
individual units from a single primary unit, <strong>the</strong> ovum. It is<br />
obvious that <strong>the</strong> truth <strong>of</strong> <strong>the</strong> first proposition in no way<br />
depends on <strong>the</strong> truth <strong>of</strong> those which follow, <strong>an</strong>d that, in fact,
164 GILBERT 0. BOURNE.<br />
<strong>the</strong> second proposition is <strong>an</strong> assumption which is made <strong>to</strong><br />
explain <strong>the</strong> first. We may make <strong>Mr</strong>. Sedgwick a present <strong>of</strong><br />
<strong>the</strong> last three, whilst we retain <strong>an</strong>d value <strong>the</strong> first.<br />
The essence <strong>of</strong> <strong>the</strong> whole question is this: are we justified<br />
in considering <strong>the</strong> elementary parts <strong>of</strong> <strong>an</strong> org<strong>an</strong>ism <strong>to</strong> be<br />
independent life units ? Before we c<strong>an</strong> <strong>an</strong>swer this, we must<br />
inquire why we do consider <strong>the</strong>m <strong>to</strong> be independent life units ?<br />
The <strong>an</strong>swer <strong>to</strong> this is probably <strong>to</strong> be found in <strong>the</strong> aphorism,<br />
which commends itself <strong>to</strong> everybody, that reproduction is<br />
discontinuous growth. From <strong>the</strong> observation that, in<br />
unicellular org<strong>an</strong>isms, division <strong>of</strong> <strong>the</strong> unit—<strong>the</strong> cell-corpuscle<br />
—leads <strong>to</strong> <strong>the</strong> liberation <strong>of</strong> a new <strong>an</strong>d independent unit, <strong>an</strong>d<br />
that in multicellular org<strong>an</strong>isms it is <strong>the</strong> liberation <strong>of</strong> <strong>an</strong><br />
independent unit—<strong>the</strong> ovum—which constitutes reproduction,<br />
it has become a settled conviction in men's minds, that division<br />
<strong>of</strong> a cell-corpuscle me<strong>an</strong>s <strong>the</strong> liberation <strong>of</strong> a new unit, that is }<br />
<strong>the</strong> setting free <strong>of</strong> a new independent <strong>being</strong>. It is this conviction<br />
which has led <strong>to</strong> <strong>the</strong> belief that <strong>the</strong> units composing a<br />
multicellular org<strong>an</strong>ism are in posse independent <strong>being</strong>s,<br />
though in esse subordinate <strong>to</strong> <strong>the</strong> whole <strong>of</strong> which <strong>the</strong>y form<br />
a part. This was <strong>the</strong> argument <strong>of</strong> Schw<strong>an</strong>n when he wrote<br />
<strong>the</strong> passage which I have quoted on p. 149, <strong>an</strong>d <strong>the</strong> argument<br />
has been taken as conclusive.<br />
But we know now that <strong>the</strong> power which Schw<strong>an</strong>n <strong>an</strong>d his<br />
followers limited <strong>to</strong> cells is inherent in pro<strong>to</strong>plasmic masses<br />
not divided in<strong>to</strong> cells. For inst<strong>an</strong>ce, if <strong>the</strong> cell-membr<strong>an</strong>e<br />
<strong>of</strong> a Coeloblastic alga is ruptured, portions <strong>of</strong> <strong>the</strong> exuded<br />
pro<strong>to</strong>plasm, provided <strong>the</strong>y contain one or more nuclei, may<br />
become, after a time, surrounded by a new cell-membr<strong>an</strong>e,<br />
grow, <strong>an</strong>d form a new pl<strong>an</strong>t.<br />
The experiments <strong>of</strong> Gruber show also, that portions <strong>of</strong><br />
Amoebae artifically separated may, provided that <strong>the</strong>y contain<br />
nuclear subst<strong>an</strong>ce, recover from <strong>the</strong> operation, <strong>an</strong>d lead <strong>an</strong><br />
independent existence;<br />
May I ask, in paren<strong>the</strong>sis, whe<strong>the</strong>r <strong>the</strong>re c<strong>an</strong> be a better<br />
illustration <strong>of</strong> <strong>the</strong> truth <strong>of</strong> <strong>the</strong> contention which I have endeavoured<br />
<strong>to</strong> establish above, that whilst a uninucleate cor-
A CRITICISM OP THE CELL-THEORY. 165<br />
puscle <strong>of</strong> pro<strong>to</strong>plasm is in esse as also in posse a unit <strong>of</strong><br />
independent vitality, a multinucleate corpuscle or mass <strong>of</strong><br />
pro<strong>to</strong>plasm is in posse composed <strong>of</strong> separate cells (units <strong>of</strong><br />
independent vitality if one chooses <strong>to</strong> call <strong>the</strong>m so) whilst still<br />
in esse a single unit <strong>of</strong> independent vitality ?<br />
To continue <strong>the</strong> subject. We now know also that division<br />
in<strong>to</strong> cells is not necessarily, though it sometimes may be,<br />
division in<strong>to</strong> units <strong>of</strong> independent vitality, but is <strong>of</strong>ten (may we<br />
not say generally ?) incomplete separation in<strong>to</strong> form elements<br />
which may indeed, under certain conditions, be completely<br />
separated, <strong>an</strong>d exhibit <strong>an</strong> independent vitality (Begonia), but<br />
under normal conditions participate in <strong>the</strong> vitality <strong>of</strong> <strong>the</strong> whole<br />
pl<strong>an</strong>t or <strong>an</strong>imal by me<strong>an</strong>s <strong>of</strong> <strong>the</strong>ir connections with <strong>the</strong>ir<br />
fellows. Hence we must conclude, as it seems <strong>to</strong> me, that <strong>the</strong><br />
elementary parts <strong>of</strong> org<strong>an</strong>isms are not independent life units<br />
in esse. They may be so in posse in m<strong>an</strong>y cases, but as<br />
differentiation <strong>an</strong>d specialization progress <strong>the</strong>y lose this power<br />
also, <strong>an</strong>d c<strong>an</strong>not, when separated from <strong>the</strong> whole <strong>of</strong> which <strong>the</strong>y<br />
form a part, exhibit independent activities.<br />
This consideration leads <strong>to</strong> <strong>the</strong> apparent paradox, that <strong>the</strong><br />
higher <strong>the</strong> org<strong>an</strong>isation <strong>the</strong> less conjunct <strong>an</strong>d, at <strong>the</strong> same<br />
time, <strong>the</strong> less independent are its parts ; <strong>the</strong> lower <strong>the</strong> org<strong>an</strong>isation<br />
<strong>the</strong> more conjunct, but also <strong>the</strong> more independent are its<br />
parts.<br />
This is a puzzle which has, for years past, exercised <strong>the</strong><br />
minds <strong>of</strong> biologists. There is, I believe, but one solution <strong>of</strong><br />
<strong>the</strong> difficulty, <strong>an</strong>d it is <strong>to</strong> be found in <strong>the</strong> physiological import<br />
<strong>of</strong> cells.<br />
But before we c<strong>an</strong> enter in<strong>to</strong> this question we must finally<br />
satisfy ourselves, as far as circumst<strong>an</strong>ces allow, about <strong>the</strong><br />
morphological concept <strong>of</strong> a cell.<br />
That <strong>the</strong> cell is a thing cognisable, <strong>an</strong>d that it is not <strong>an</strong><br />
unreal figment, due <strong>to</strong> imperfect observation or <strong>to</strong> hopelessly<br />
prejudiced interpretation <strong>of</strong> our observations, as <strong>Mr</strong>. Sedgwick<br />
would make us believe, I will try <strong>to</strong> show.<br />
•;<br />
A cell is a " body," <strong>an</strong>d <strong>the</strong>refore <strong>an</strong> external cause <strong>to</strong> which<br />
we attribute our sensatipns. I would submit that, without
166 GILBERT C. BOURNE.<br />
prejudice <strong>to</strong> <strong>the</strong> metaphysical st<strong>an</strong>dpoint, we must conceive<br />
that what is capable <strong>of</strong> giving rise in us <strong>to</strong> such very distinct<br />
sensations, must have a real existence. I am referring now <strong>to</strong><br />
<strong>the</strong> component'parts <strong>of</strong> <strong>the</strong> tissues <strong>of</strong> higher <strong>an</strong>imals <strong>an</strong>d pl<strong>an</strong>ts,<br />
<strong>an</strong>d not <strong>to</strong> unicellular org<strong>an</strong>isms.<br />
If, <strong>the</strong>n, <strong>the</strong> thing has existence, it must have attributes;<br />
we must be able <strong>to</strong> affirm something <strong>of</strong> it. What we have <strong>to</strong><br />
affirm is not <strong>the</strong> attributes <strong>of</strong> this cell or <strong>of</strong> that cell, but <strong>of</strong><br />
cells in general. We have <strong>to</strong> give expression <strong>to</strong> a morphological<br />
idea, in <strong>the</strong> sense in which Goe<strong>the</strong> used <strong>the</strong> word<br />
morphological. Our concept <strong>of</strong> a cell must be <strong>an</strong> " Allgemeines<br />
bild," <strong>the</strong> generalised idea <strong>of</strong> a cell, derived from our experience<br />
<strong>of</strong> m<strong>an</strong>y kinds <strong>of</strong> cells. I have already shown, at<br />
sufficient length, that we must now regard something <strong>of</strong> <strong>the</strong><br />
nature <strong>of</strong> a nucleus as <strong>an</strong> essential component <strong>of</strong> all cells, but<br />
as <strong>the</strong> concept <strong>of</strong> a nucleus as a central org<strong>an</strong>ised body is not<br />
applicable <strong>to</strong> all cells, I would widen Max Schulze's definition<br />
by saying that "a cell is a corpuscle <strong>of</strong> pro<strong>to</strong>plasm, which<br />
contains a specialised element, nuclein." This is a sufficiently<br />
comprehensive statement <strong>of</strong> our " Allgemeines bild," though<br />
I c<strong>an</strong>not pretend that it is not open <strong>to</strong> objection.<br />
<strong>Cell</strong>s, as thus defined, are not only <strong>of</strong> various kinds, but<br />
<strong>the</strong>y are variously compounded <strong>to</strong>ge<strong>the</strong>r. We may, by <strong>the</strong><br />
process <strong>of</strong> dicho<strong>to</strong>mous division, classify <strong>the</strong>m, according <strong>to</strong><br />
<strong>the</strong>ir relations <strong>to</strong> o<strong>the</strong>r cells, as discrete <strong>an</strong>d concrescent.<br />
By discrete cells, I me<strong>an</strong> those whose pro<strong>to</strong>plasm is not<br />
in union with that <strong>of</strong> <strong>an</strong>y o<strong>the</strong>r corpusde.<br />
By concrescent cells, I me<strong>an</strong> corpuscles whose pro<strong>to</strong>plasm<br />
is in union with that <strong>of</strong> o<strong>the</strong>r corpuscles.<br />
Discrete cells may fur<strong>the</strong>r be divided in<strong>to</strong>:<br />
Independent cells, living wholly apart from one <strong>an</strong>o<strong>the</strong>r,<br />
or separated by <strong>an</strong> appreciable interval <strong>of</strong> space, e. g. uninucleate<br />
Pro<strong>to</strong>zoa, <strong>the</strong> mature ovum, leucocytes.<br />
Coherent cells, which are in close apposition <strong>to</strong> o<strong>the</strong>rs,<br />
but not org<strong>an</strong>ically in union with <strong>the</strong>m, e. g. <strong>the</strong> blas<strong>to</strong>meres <strong>of</strong><br />
m<strong>an</strong>y developing embryos.<br />
Concrescent cells may also be fur<strong>the</strong>r divided in<strong>to</strong> :
A CRITICISM OF THE OELL-THEORT. 167<br />
Continuous cells, whose pro<strong>to</strong>plasm is fused but whose<br />
nuclei are separate, e.g. Myxomycetes, Cceloblastae,<br />
Opaliua.<br />
Conjunct cells, those which having a pro<strong>to</strong>plasmic body<br />
<strong>of</strong> definite outline are united inter se by fine bonds <strong>of</strong> pro<strong>to</strong>plasm,<br />
e. g. vegetable tissue cells, epi<strong>the</strong>lial cells <strong>of</strong> m<strong>an</strong>y<br />
<strong>an</strong>imals; meseuchyme cells, &c.<br />
Experience shows us that independent cells may, in process<br />
<strong>of</strong> growth, give rise <strong>to</strong> coherent cells, continuous cells, conjunct<br />
cells, or <strong>to</strong> all three <strong>to</strong>ge<strong>the</strong>r, <strong>an</strong>d that coherent, continuous,<br />
or conjunct cells may, <strong>an</strong>d in fact do, give rise <strong>to</strong><br />
independent cells. As thus stated, c<strong>an</strong> <strong>the</strong>re be a better<br />
illustration <strong>of</strong> von Sachs's principle that cell-formation is <strong>an</strong><br />
accomp<strong>an</strong>iment <strong>of</strong> growth ?<br />
It will be observed that, in adhering <strong>to</strong> <strong>the</strong> present terminology,<br />
I am obliged <strong>to</strong> classify org<strong>an</strong>isms usually (though not<br />
always) called unicellular as multicellular. I have tried <strong>to</strong><br />
escape from this necessity, but <strong>the</strong> limitations <strong>of</strong> l<strong>an</strong>guage<br />
compel me <strong>to</strong> it. I should be grateful for a better <strong>an</strong>d more<br />
logical definition.<br />
The view <strong>of</strong> <strong>Mr</strong>. Sedgwick—if I do not misrepresent him—<br />
is this, that <strong>the</strong>re are no coherent cells; that all which I have<br />
classified as continuous <strong>an</strong>d conjunct cells are not cells, but<br />
tracts <strong>of</strong> pro<strong>to</strong>plasm; that <strong>the</strong> only cell, sensu stric<strong>to</strong>, is<br />
<strong>the</strong> independent cell, <strong>an</strong>d that morphologically <strong>an</strong>d physiologically<br />
it is <strong>of</strong> no consequence.<br />
I have already shown that <strong>the</strong>re are cells which we must<br />
regard as coherent. I c<strong>an</strong>not, for reasons which I will explain<br />
directly, consider <strong>the</strong> independent cell <strong>of</strong> no consequence, <strong>an</strong>d<br />
<strong>the</strong> difference between us as <strong>to</strong> conjunct cells is simply this ;<br />
Are <strong>the</strong>y <strong>to</strong> be regarded as one or m<strong>an</strong>y ? I c<strong>an</strong>, perhaps, best<br />
express this difference by <strong>an</strong> illustration.<br />
Is a house <strong>to</strong> be regarded as one room or composed <strong>of</strong><br />
separate rooms ? A room is a certain portion <strong>of</strong> space enclosed<br />
by walls, ceiling, <strong>an</strong>d floor; but it is also in connection, by<br />
me<strong>an</strong>s <strong>of</strong> <strong>the</strong> door, with o<strong>the</strong>r similar rooms. Is it, <strong>the</strong>n, not<br />
a separate room, but part <strong>of</strong> a larger room ? Or if I shut <strong>the</strong>
168 GILBERT 0. BOTJENE.<br />
door is it a room, <strong>an</strong>d if I open <strong>the</strong> door is it no longer a<br />
room ? The subject might be argued with much ingenuity,<br />
but <strong>the</strong> final <strong>an</strong>swer is this—that " room " <strong>an</strong>d " cell " are<br />
terms which give expressions <strong>to</strong> certain states <strong>of</strong> our consciousness,<br />
<strong>an</strong>d for practical purposes <strong>the</strong>y are very useful terms<br />
indeed. Where distinct states <strong>of</strong> consciousness are called up,<br />
<strong>of</strong> such a nature as <strong>to</strong> give rise <strong>to</strong> ideas <strong>of</strong> particularity, it<br />
is a mere quibble <strong>to</strong> argue that <strong>the</strong> apparent parts are actually<br />
merged in a whole. A cell is none <strong>the</strong> less a cell, in <strong>the</strong> sense<br />
<strong>of</strong> a thing distinct in itself, because it is conjunct with its<br />
fellow cell, th<strong>an</strong> my room is <strong>the</strong> less a room because it has<br />
one door opening in<strong>to</strong> <strong>an</strong> adjoining room <strong>an</strong>d <strong>an</strong>o<strong>the</strong>r opening<br />
in<strong>to</strong> <strong>the</strong> passage.<br />
Yet <strong>the</strong>re is something more th<strong>an</strong> a verbal quibble in <strong>Mr</strong>.<br />
<strong>Sedgwick's</strong> contention. He would have it that in <strong>the</strong> case <strong>of</strong><br />
mesenchyme it is incorrect <strong>to</strong> say that it is a number <strong>of</strong> stellate<br />
cells joined <strong>to</strong> one <strong>an</strong>o<strong>the</strong>r by <strong>the</strong>ir processes. For him<br />
<strong>the</strong> correct description is, " a pro<strong>to</strong>plasmic reticulum with<br />
nuclei at <strong>the</strong> nodes." Does he accept <strong>the</strong> logical consequences<br />
<strong>of</strong> this, <strong>an</strong>d say <strong>of</strong> <strong>the</strong> epi<strong>the</strong>lial cells <strong>of</strong> <strong>the</strong> Salam<strong>an</strong>der or <strong>of</strong><br />
unstriped muscle fibres that <strong>the</strong>y are pro<strong>to</strong>plasmic reticula<br />
with nuclei at <strong>the</strong>ir nodes? And if so, how does he explain<br />
<strong>the</strong> fact that, in <strong>the</strong> one case <strong>an</strong>d in <strong>the</strong> o<strong>the</strong>r, <strong>the</strong> elements<br />
when absolutely isolated by appropriate methods show a remarkably<br />
const<strong>an</strong>t <strong>an</strong>d characteristic form ? Were <strong>the</strong>y what<br />
he describes, rupture <strong>of</strong> <strong>the</strong> internodes <strong>of</strong> <strong>the</strong> reticulum would<br />
result in amorphous lumps <strong>of</strong> pro<strong>to</strong>plasm, not in units <strong>of</strong><br />
characteristic form. It is <strong>the</strong> const<strong>an</strong>cy <strong>of</strong> <strong>the</strong> various forms<br />
<strong>of</strong> cells which convinces morphologists <strong>of</strong> <strong>the</strong>ir individuality<br />
as form elements, <strong>an</strong>d all <strong>the</strong> arguments which <strong>Mr</strong>. Sedgwick<br />
or <strong>an</strong>ybody else may choose <strong>to</strong> bring forward will not convince<br />
<strong>the</strong> m<strong>an</strong> who goes in<strong>to</strong> a labora<strong>to</strong>ry, makes a few maceration<br />
preparations, <strong>an</strong>d studies <strong>the</strong> results for himself.<br />
Thus a tissue formed <strong>of</strong> conjunct cells is made up <strong>of</strong> m<strong>an</strong>y<br />
<strong>an</strong>d not <strong>of</strong> one, <strong>an</strong>d as a form concept <strong>the</strong> cell holds its ground<br />
<strong>an</strong>d, pace <strong>Mr</strong>. Sedgwick, it will continue <strong>to</strong> hold its ground<br />
against all comers.
A CRITICISM OF THE CELL-THEORY. 169<br />
As a physiological concept it is hardly less useful, though<br />
reflection may induce us <strong>to</strong> ab<strong>an</strong>don <strong>the</strong> " cell-republic"<br />
<strong>the</strong>ory, as, indeed, it has been tacitly ab<strong>an</strong>doned by m<strong>an</strong>y.<br />
I take it that <strong>the</strong> scheme <strong>of</strong> von Sachs very nearly expresses,<br />
in general terms, <strong>the</strong> physiological import<strong>an</strong>ce <strong>of</strong> <strong>the</strong> cell.<br />
An org<strong>an</strong>ism is a pro<strong>to</strong>plasmic body, coherent in itself, which<br />
grows, <strong>an</strong>d as it grows it is divided by cleavage in<strong>to</strong> innumerable<br />
corpuscles, <strong>an</strong>d it appears that <strong>the</strong> more vigorously<br />
this formati<strong>an</strong> <strong>of</strong> corpuscles proceeds with <strong>the</strong> nutrition <strong>of</strong> <strong>the</strong><br />
org<strong>an</strong>ism, <strong>the</strong> higher also is <strong>the</strong> development attained by <strong>the</strong><br />
<strong>to</strong>tal org<strong>an</strong>isation. Nor does this statement st<strong>an</strong>d in <strong>an</strong>y contradiction<br />
<strong>to</strong> <strong>the</strong> original <strong>the</strong>ory <strong>of</strong> Schw<strong>an</strong>n, from whom I<br />
may quote two more passages : "The elementary parts <strong>of</strong> all<br />
tissues are formed <strong>of</strong> cells, in <strong>an</strong> <strong>an</strong>alogous though very<br />
diversified m<strong>an</strong>ner, so that it may be asserted that <strong>the</strong>re is<br />
one universal principle <strong>of</strong> development for <strong>the</strong> elementary<br />
parts <strong>of</strong> org<strong>an</strong>isms, however different, <strong>an</strong>d that this principle<br />
is <strong>the</strong> formation <strong>of</strong> cells." And again, he says <strong>of</strong> <strong>the</strong> relations<br />
<strong>of</strong> cells <strong>to</strong> one <strong>an</strong>o<strong>the</strong>r, " Each cell is within certain limits <strong>an</strong><br />
individual, <strong>an</strong> independent whole. The vital phenomena <strong>of</strong><br />
one are repeated, entirely or in part, in all <strong>the</strong> rest. These<br />
individuals, however, are not r<strong>an</strong>ged side by side as a mere<br />
aggregate, but so. operate <strong>to</strong>ge<strong>the</strong>r in a m<strong>an</strong>ner unknown <strong>to</strong><br />
us, as <strong>to</strong> produce a harmonious whole." It should be remembered<br />
that Schw<strong>an</strong>n regarded cells as so m<strong>an</strong>y separate vesicles,<br />
<strong>an</strong>d when allow<strong>an</strong>ce is made for this error, <strong>the</strong> second<br />
part <strong>of</strong> <strong>the</strong> last passage must be allowed <strong>to</strong> have great signific<strong>an</strong>ce.<br />
The subordination <strong>of</strong> <strong>the</strong> parts <strong>to</strong> <strong>the</strong> harmonious<br />
whole, leading <strong>to</strong> <strong>the</strong> loss <strong>of</strong> individuality <strong>of</strong> <strong>the</strong> parts, in<br />
<strong>an</strong>imal tissues, was insisted on by Hackel in his ' Generelle<br />
Morphologic' The first <strong>of</strong> <strong>the</strong> two sentences which I have<br />
quoted from Schw<strong>an</strong>n is even more true <strong>to</strong>-day th<strong>an</strong> when it<br />
was written, for we have got rid <strong>of</strong> <strong>the</strong> cell-forming matrix,<br />
<strong>the</strong> cy<strong>to</strong>blastema ; <strong>an</strong>d I would wish <strong>to</strong> insist on this passage<br />
as expressing in <strong>the</strong> clearest possible l<strong>an</strong>guage <strong>the</strong> cell-<strong>the</strong>ory<br />
as we underst<strong>an</strong>d it <strong>to</strong>-day.<br />
From this st<strong>an</strong>dpoint we c<strong>an</strong> see, obscurely it may be, why
170 GILBERT 0. BOURNE.<br />
cell-formation accomp<strong>an</strong>ies differentiation with growth <strong>of</strong> <strong>the</strong><br />
mass, <strong>an</strong>d why specialisation is not possible in continuous<br />
tracts <strong>of</strong> pro<strong>to</strong>plasm. For, as <strong>Mr</strong>. Sedgwick himself admits,<br />
in a continuous mass <strong>of</strong> pro<strong>to</strong>plasm, ch<strong>an</strong>ges <strong>of</strong> molecular<br />
constitution in <strong>an</strong>y one part would in time spread through<br />
<strong>the</strong> whole, so that a differentiation <strong>of</strong> one part would in time<br />
be impressed on all <strong>the</strong> o<strong>the</strong>r parts, <strong>an</strong>d physiological division<br />
<strong>of</strong> labour would be out <strong>of</strong> <strong>the</strong> question. The fact that in <strong>the</strong><br />
Pro<strong>to</strong>zoa <strong>the</strong>re is differentiation within <strong>the</strong> limits <strong>of</strong> a single<br />
corpuscle presents no greater difficulty th<strong>an</strong> <strong>the</strong> fact that in<br />
<strong>the</strong> epi<strong>the</strong>lio-muscular cells <strong>of</strong> Coelenterates, or <strong>the</strong> similar<br />
cells in Nema<strong>to</strong>des, <strong>the</strong>re is differentiation within <strong>the</strong> limits <strong>of</strong><br />
<strong>the</strong> cell.<br />
Again, metabolism in a large mass is greatly facilitated by<br />
its <strong>being</strong> broken up. As von Sachs says, " It is very intelligible<br />
that not only <strong>the</strong> solidity but also <strong>the</strong> shutting <strong>of</strong>f <strong>of</strong> various<br />
products <strong>of</strong> metabolism, <strong>the</strong> conduction <strong>of</strong> <strong>the</strong> sap from place<br />
<strong>to</strong> place, <strong>an</strong>d so forth, must attain greater perfection if <strong>the</strong><br />
whole subst<strong>an</strong>ce <strong>of</strong> a pl<strong>an</strong>t is divided up by numerous tr<strong>an</strong>sverse<br />
<strong>an</strong>d longitudinal partitions in<strong>to</strong> cell chambers." The same<br />
thing applies, mutatis mut<strong>an</strong>dis, <strong>to</strong> <strong>an</strong>imals, <strong>an</strong>d it is not<br />
difficult <strong>to</strong> see that <strong>the</strong> difference between holozoic <strong>an</strong>d holophytic<br />
nutrition makes it impossible for. <strong>the</strong> <strong>an</strong>imal <strong>to</strong> grow<br />
<strong>to</strong> a large mass without division in<strong>to</strong> cells, whilst such growth<br />
is possible in <strong>the</strong> case <strong>of</strong> pl<strong>an</strong>ts which, like Codium <strong>an</strong>d<br />
Caulerpa, live in water, or like Botrydium in damp earth.<br />
It is known that <strong>the</strong> spaces between epi<strong>the</strong>lial cells which<br />
are traversed by <strong>the</strong> connecting str<strong>an</strong>ds <strong>of</strong> pro<strong>to</strong>plasm, <strong>an</strong>d<br />
were formerly supposed <strong>to</strong> be occupied by a cement subst<strong>an</strong>ce,<br />
are in reality lymph spaces, <strong>an</strong>d this gives us some insight in<strong>to</strong><br />
<strong>the</strong> import<strong>an</strong>ce <strong>of</strong> <strong>the</strong> cell structure in <strong>an</strong>imal org<strong>an</strong>isation.<br />
The formation <strong>of</strong> cells with spaces between admits <strong>of</strong> nutrient<br />
fluid <strong>being</strong> brought <strong>to</strong> <strong>the</strong> very threshold <strong>of</strong> each constituent<br />
corpuscle <strong>of</strong> <strong>the</strong> org<strong>an</strong>ism. (See on this subject Th. Cohn,<br />
R. Heidenhain, Paulicki, Nicolas, Werner, <strong>an</strong>d o<strong>the</strong>rs.)<br />
Whilst <strong>the</strong> necessities <strong>of</strong> cohesion, solidity, <strong>an</strong>d tr<strong>an</strong>smission<br />
<strong>of</strong> stimuli may explain <strong>the</strong> conjunct nature <strong>of</strong> so m<strong>an</strong>y tissue
A ORTTIOISM OP THE OELL-THEORY. 171<br />
cells, recent researches on cell lineages may perhaps give us<br />
a clue <strong>to</strong> <strong>the</strong> interpretation <strong>of</strong> <strong>the</strong> fact that blas<strong>to</strong>meres are<br />
in so m<strong>an</strong>y cases, no more th<strong>an</strong> coherent. For it is noticeable<br />
that wherever cell lineages, with marked isolation <strong>of</strong> <strong>the</strong> blas<strong>to</strong>meres,<br />
have been described, <strong>the</strong>re is a decided tendency <strong>to</strong> <strong>the</strong><br />
precocious development <strong>of</strong> org<strong>an</strong>s, or, at <strong>an</strong>y rate, <strong>to</strong> <strong>the</strong> precocious<br />
isolation <strong>of</strong> <strong>the</strong> primordia (Anlage) <strong>of</strong> org<strong>an</strong>s.<br />
It seems probable that <strong>the</strong> discrete condition <strong>of</strong> <strong>the</strong> blas<strong>to</strong>meres<br />
is connected with <strong>the</strong> fact, <strong>to</strong> which I alluded in <strong>the</strong><br />
earlier part <strong>of</strong> this essay, that <strong>the</strong>y are, from <strong>the</strong> very outset,<br />
specialised. They have each a definite molecular constitution<br />
different from <strong>the</strong> o<strong>the</strong>rs, <strong>an</strong>d, in figurative l<strong>an</strong>guage, a<br />
limited part <strong>to</strong> perform, which <strong>the</strong>y could not perform <strong>to</strong><br />
adv<strong>an</strong>tage if <strong>the</strong>y were conjunct with <strong>the</strong> o<strong>the</strong>r blas<strong>to</strong>meres<br />
<strong>an</strong>d shared in <strong>the</strong>ir different molecular constitution. But<br />
this is a subject which I must leave for a future occasion when<br />
I discuss <strong>the</strong> validity <strong>of</strong> von Baer's law <strong>of</strong> development.<br />
( I have travelled in this essay over a great deal <strong>of</strong> ground,<br />
<strong>an</strong>d I have necessarily had <strong>to</strong> <strong>to</strong>uch more lightly on m<strong>an</strong>y<br />
<strong>to</strong>pics th<strong>an</strong> I should have wished. I hope that I may at<br />
least have succeeded in presenting my arguments in a m<strong>an</strong>ner<br />
which will make <strong>the</strong>m clear <strong>to</strong> my readers, <strong>an</strong>d that I have not<br />
been <strong>to</strong>o discursive. Starting from <strong>Mr</strong>. <strong>Sedgwick's</strong> propositions<br />
<strong>an</strong>d accusations, I have tried <strong>to</strong> show what is or was <strong>the</strong> exact<br />
extent <strong>an</strong>d me<strong>an</strong>ing <strong>of</strong> <strong>the</strong> cell-<strong>the</strong>ory ; I have tried <strong>to</strong> examine<br />
it <strong>an</strong>d show how much was good <strong>an</strong>d how much bad, <strong>an</strong>d I<br />
have finally been led <strong>to</strong> <strong>the</strong> conclusion—which is not quite<br />
what I proposed <strong>to</strong> myself at <strong>the</strong> outset—that <strong>the</strong> cell concept<br />
is a valuable expression <strong>of</strong> our experience <strong>of</strong> org<strong>an</strong>ic life, both<br />
morphologically <strong>an</strong>d physiologically, but that in higher org<strong>an</strong>isms<br />
cells are much what von Sachs declares <strong>the</strong>m <strong>to</strong><br />
be, not independent life units (Lebenseinzelheiten), but a<br />
phenomenon so general as <strong>to</strong> be <strong>of</strong> <strong>the</strong> highest signific<strong>an</strong>ce;<br />
<strong>the</strong>y are <strong>the</strong> const<strong>an</strong>t <strong>an</strong>d definite expression <strong>of</strong> <strong>the</strong> formative<br />
forces which reside in so high a degree in org<strong>an</strong>ic matter.<br />
Lest I should appear <strong>to</strong> have minimised <strong>the</strong> import<strong>an</strong>ce <strong>of</strong><br />
<strong>the</strong> cell <strong>to</strong>o much, let me conclude by saying, that nothing
172 GILBERT 0. BOURNE.<br />
which has appeared above calls in<strong>to</strong> question that great feature<br />
<strong>of</strong> <strong>an</strong>imal <strong>an</strong>d pl<strong>an</strong>t development which most impresses <strong>the</strong><br />
biological student, viz. that org<strong>an</strong>ic growth is a cycle, beginning<br />
in <strong>the</strong> single cell, <strong>an</strong>d returning <strong>to</strong> <strong>the</strong> single cell again. And<br />
<strong>the</strong>refore, in a limited sense, <strong>the</strong> cell is par excellence <strong>the</strong><br />
unit <strong>of</strong> life. Its growth takes various forms <strong>an</strong>d shows m<strong>an</strong>y<br />
complexities, but whatever <strong>the</strong> form, however great <strong>the</strong> complexity,<br />
it is a progress from <strong>the</strong> state <strong>of</strong> <strong>an</strong> independent<br />
corpuscle, through a state <strong>of</strong> m<strong>an</strong>y coherent, or continuous,<br />
or conjunct, interdependent corpuscles, back again <strong>to</strong> <strong>the</strong> state<br />
<strong>of</strong> a single independent corpuscle.<br />
This was <strong>the</strong> great adv<strong>an</strong>ce made by Remak on <strong>the</strong> <strong>the</strong>ory<br />
<strong>of</strong> Schw<strong>an</strong>n, <strong>an</strong>d summed up in Virchow's aphorism, which I<br />
believe <strong>to</strong> be universally true. For Schw<strong>an</strong>n did not hold that<br />
cells are <strong>the</strong> ultimate basis <strong>of</strong> life: he held that <strong>the</strong>y are<br />
formed, as a crystal is formed out <strong>of</strong> its mo<strong>the</strong>r liquor, from a<br />
structureless matrix, <strong>the</strong> cy<strong>to</strong>blastema. To some such <strong>the</strong>ory<br />
<strong>Mr</strong>. Sedgwick wishes <strong>to</strong> take us back again, for his " pale <strong>an</strong>dat<br />
first sparse reticulum " bears a most suspicious resembl<strong>an</strong>ce<br />
<strong>to</strong> <strong>the</strong> exploded cy<strong>to</strong>blastema. " The development <strong>of</strong> nerves,"<br />
he says, " is not <strong>an</strong> outgrowth from certain central cells, but<br />
is a differentiation <strong>of</strong> a subst<strong>an</strong>ce which was already in<br />
position." And earlier in his article, referring <strong>to</strong> <strong>the</strong> growth<br />
<strong>an</strong>d extension <strong>of</strong> <strong>the</strong> mesoblast between epiblast <strong>an</strong>d hypoblast,<br />
he says : " What are <strong>the</strong> facts ? The space between <strong>the</strong> layers<br />
is never empty. It is always traversed by str<strong>an</strong>ds <strong>of</strong> a pale<br />
tissue connecting <strong>the</strong> various layers, <strong>an</strong>d <strong>the</strong> growth which<br />
does take place between <strong>the</strong> layers is not a formation <strong>of</strong> cells<br />
but <strong>of</strong> nuclei, which move away from <strong>the</strong>ir place <strong>of</strong> origin<br />
<strong>an</strong>d take up <strong>the</strong>ir position in this pale <strong>an</strong>d at first sparse<br />
reticulum."<br />
But surely nobody ever affirmed that <strong>the</strong> space between <strong>the</strong><br />
layers was empty except in <strong>the</strong> sense that it is devoid <strong>of</strong><br />
cellular structures. It is well known that it is filled with a<br />
coagulable fluid, <strong>an</strong>d it is worthy <strong>of</strong> remark that coagulable<br />
fluids, treated with <strong>the</strong> reagents now most in use, frequently<br />
form a reticulum <strong>of</strong> pale non-staining subst<strong>an</strong>ce. I c<strong>an</strong> speak
A CRITICISM OF THE CELL-THEORY. 173<br />
from experience, for not long since I was much puzzled by<br />
such a reticulum, <strong>an</strong>d had I been less cautious I should have<br />
published, as a great morphological discovery, statements which<br />
rested on a wholly insufficient basis <strong>of</strong> experience. The subject<br />
requires fur<strong>the</strong>r investigation, <strong>an</strong>d <strong>the</strong> most that one c<strong>an</strong> say<br />
now is, that it is possible that <strong>Mr</strong>. Sedgwick, good observer as<br />
he is, may have been mistaken. And he will pardon my<br />
observing that <strong>the</strong> things which he states are not " facts."<br />
They are his own inferences from his own individual observations,<br />
<strong>an</strong>d will require very abund<strong>an</strong>t confirmation before <strong>the</strong>y<br />
c<strong>an</strong> take r<strong>an</strong>k as what we agree <strong>to</strong> regard as " facts." All <strong>the</strong><br />
" facts " we have at present, i. e. <strong>the</strong> accumulated observations<br />
<strong>of</strong> hundreds <strong>of</strong> highly-trained <strong>an</strong>d able observers, are fundamentally<br />
opposed <strong>to</strong> <strong>an</strong>y such account <strong>of</strong> pro<strong>to</strong>plasmic growth<br />
apart from nuclear formation as <strong>Mr</strong>. Sedgwick gives us. But<br />
<strong>the</strong>re is <strong>an</strong>o<strong>the</strong>r way <strong>of</strong> looking at it, namely, that he has only<br />
overstated his case, <strong>an</strong>d that <strong>the</strong> growth <strong>of</strong> <strong>the</strong> tissues in<br />
question resembles <strong>the</strong> apparent creeping motion <strong>of</strong> <strong>the</strong> plasmodia<br />
<strong>of</strong> <strong>the</strong> Myxomycetes. That this may be <strong>the</strong> case is<br />
supported by a study <strong>of</strong> <strong>Mr</strong>. Asshe<strong>to</strong>n's recent account <strong>of</strong> <strong>the</strong><br />
growth <strong>of</strong> <strong>the</strong> mesoblast <strong>an</strong>d <strong>of</strong> <strong>the</strong> inner layer <strong>of</strong> <strong>the</strong> epiblast<br />
in <strong>the</strong> embryo <strong>of</strong> <strong>the</strong> rabbit. It presents no <strong>the</strong>oretical difficulties,<br />
but it should be remarked that <strong>Mr</strong>. Asshe<strong>to</strong>n figures<br />
numerous nuclei at <strong>the</strong> very edge <strong>of</strong> <strong>the</strong> growing part <strong>of</strong> his<br />
reticula, which is conson<strong>an</strong>t with what we know <strong>of</strong> pro<strong>to</strong>plasmic<br />
growth in o<strong>the</strong>r cases, but not with <strong>Mr</strong>. <strong>Sedgwick's</strong><br />
account.<br />
But if <strong>Mr</strong>. Sedgwick c<strong>an</strong> prove that <strong>the</strong> reticulum is <strong>the</strong>re<br />
<strong>an</strong>d that it grows <strong>an</strong>d spreads far from <strong>the</strong> nuclei which subsequently<br />
migrate in<strong>to</strong> it, he must not suppose, as he is<br />
apparently so ready <strong>to</strong> assume, that <strong>the</strong> inveterate prejudice<br />
<strong>of</strong> morphologists will prevent <strong>the</strong>ir accepting his conclusions<br />
because <strong>of</strong> <strong>the</strong>ir <strong>the</strong>oretical difficulties. If his case is proved,<br />
it will be accepted, but he must prove it up <strong>to</strong> <strong>the</strong> hilt.<br />
And if he does prove it, what <strong>the</strong>n ? It will be <strong>an</strong> isolated<br />
case, <strong>of</strong> secondary signific<strong>an</strong>ce: merely <strong>an</strong>o<strong>the</strong>r addition <strong>to</strong><br />
our experience <strong>of</strong> <strong>the</strong> very various phenomena displayed in
174 GILBERT C. BOURNE.<br />
org<strong>an</strong>ic growth. For thous<strong>an</strong>ds <strong>of</strong> inst<strong>an</strong>ces point <strong>to</strong> <strong>the</strong> fact<br />
that normal growth is effected in a very different way, by<br />
mi<strong>to</strong>tic division <strong>of</strong> <strong>the</strong> nucleus preceding <strong>an</strong>d directing <strong>the</strong><br />
formation <strong>of</strong> a discrete or concrescent cell-corpuscle. The<br />
recent researches <strong>of</strong> cy<strong>to</strong>logists are <strong>to</strong>o m<strong>an</strong>y, <strong>to</strong>o good <strong>of</strong><br />
<strong>the</strong>ir kind, <strong>an</strong>d <strong>to</strong>o consistent <strong>to</strong> admit <strong>of</strong> <strong>an</strong>y o<strong>the</strong>r conclusion.