Picture - Cosmic Polymath

THE REPRODUCTIVE ELEMENTS OF PLANTS AND ANIMALS 97
physical forces) in certain cases overcome gravitation equally with the vital forces, but it does not follow from this
that gravitation as a power is extinguished. When gravitation (and this remark appUes to all the physical forces)
is useful in building up the organism, it is employed by nature in conjunction with the vital forces ; and when
capillarity, osmosis, &c., are more convenient, they are preferred. The vital and physical forces must be regarded
in their totality, nor must the object in view be lost sight of. Natural laws and forces (vital, chemical, and
physical) act and react upon each other ;
and though at times some are inoperative, they are not annihilated, neither
are they opposed when the final effect to be produced is taken into account. Organised structures are built up in
accordance with natural laws. Thus, their parts and particles consist of substances which naturally have a
chemical afiinity for each other ; those substances absorb and respire—that is, take in and give off fluids ; they
exhibit, for the most part, capillary spaces and interspaces in their interior ; they have weight, porosity, elasticity,
and various other purely physical properties. In this way chemical affinity, osmosis, capillarity, gravitation, &c.,
have free play, and each in turn assists not only in forming and maintaining the body, but also in disintegrating
it. The vital forces, if I may be allowed the expression, use and abuse the physical ones. They do not, they
cannot, annihilate them. As well may we say the vital forces annihilate matter.
THE REPRODUCTIVE ELEMENTS OF PLANTS AND ANIMALS ESSENTIALLY AND
FUNDAMENTALLY DIFFER FROM THE BEGINNING
Whatever may be said regarding the ultimate composition of protoplasm, the grand fact remains, that the
germs and seeds of plants and the eggs of animals, apparently homogeneous and identical, invariably produce not
only their own kind, but, during the process of development, substances which are altogether dissimilar. Even man,
with his wealth of imagination and thought, is the product of an egg, which to the eye of the microscopist and
chemist is, as to its several parts, homogeneous and identical. Yet this egg, with its several parts placed in exactly
the same conditions, produces the tender pulp of the brain, the fiaccid muscles, the tough tendons, the elastic carti-
lages, the hard bones, the stiU harder teeth, the enamel, a substance nearly as brittle as glass, and in due time the
several secretions, the major portion of which is composed of water. To these are to be added the external skin,
with its hair, nails, &c. ; the internal skin or mucous membrane, with its numerous glands ; the secreting and
excreting organs ; the nerves ; the lymphatics ; and the blood-vessels, with their contained blood, so rich, so
complex, so marvellous in composition. These various products, so diverse in form, composition, and function,
are, we know, the product of an egg. Shall we be told, or, if told, shall we believe, that this egg is homogeneous
and identical in all its parts and particles ? Identical these parts may be to the eye of sense, but to the eye of
reason they are not so. Matter similarly constituted, similarly disposed, and similarly conditioned—that is, placed
under precisely similar circumstances—behaves in precisely the same manner ; in other words, all the parts are
infiuenced afike. If fife had to operate on absolutely identical matter, the living mass would be simply homogeneous
that is, undifferentiated ; and if undifferentiated, it would have no power to build up either a plant or an animal.
It is impossible to produce muscle, bone, brain, &c., from matter identical in ultimate composition. In the germ,
the seed, the egg, even from the first, there is differentiation, actual or potential.-' The first embryonic changes
are the result of this differentiation. It is this which enables the different parts of the embryo to attract and
assinailate different substances and to build up different tissues. One embryonic change involves another, and
gradually the individual is developed, each according to its kind. The weaver may not produce a web dissimilar in
texture and pattern in the absence of dissimilar elements. He must be supplied with the warp, the woof, and the
varied pigment. A queen-bee may be formed from an ordinary bee grub by changing the quantity and quality
of its food, but no amount of change of diet can produce from the same grub a dragon-fly or a locust.
In making these statements regarding the non-identity of protoplasm, bioplasm, and the several parts of
^ Mr. Herbert Spencer, in his " Principles of Biology," expressed the belief that in reproduction the cell must be regarded as the morpho-
logical unit, but that in addition there must be a chemical unit consisting of the simplest combination of molecules capable of displaying life.
Others, who regarded the nucleus as the most important part of the cell, discovered that by the employment of suitable dyes one portion of the
nucleus could he distinguished from all the other parts. This they designated the chromatin. The chromatin, it was found, could he broken up into
a number of rod-like bodies, which were designated chromosmies. The chromosomes, when stained, were found in turn to be compound and
divisible into microsomes. This much could be demonstrated by the aid of the microscope with stained nuclei : when its powers failed, Professor
Weismann, by a process of reasoning, inferred that each of the microsomes consisted of a number of still smaller bodies, which he called determinants.
The determinants Weismann regarded as the structures forming the germ-plasm which decided the nature and character of the adult organism.
Weismann went further, and assumed that not even the determinants constituted the ultimate living elements. The detei-minants, he believed,
were further resolvable into biophores. Weismann, who has done much to expiscate this most involved and diihcult subject, was by no means the
first to deal with it in a more or less exhaustive manner. It has been a veritable bone of contention for over thirty years—each author employing
his own nomenclature.
From the foregoing it will be seen that the reproductive cell is by no means a simple structure, and that it is seen to be more complex in
proportion as our opportunities gf investigating it inoreas?,
VOL. I.
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