Some Problems of Reproduction: a Comparative Study of ...

SOMB PROBLEMS OF REPRODUCTION. 69
as in karyogamy. And this very feat has been accomplished ;
for the Hertwigs some years ago showed that Echinoderm
eggs when shaken up in sea water break into fragments ; and
observed a spermatozoon entering such a non-nucleated fragment
and segmenting therein, like the zygote segmentationnucleus.
Since then, as O. Hertwig recalls in the above-cited
paper, 1 Boveri has repeated the observations, and proved that
the normal tnorula was formed and developed into a larva. I
do not see how this is consistent with any theory of karyogamy
but Biitschli's—that it is a process of rejuvenescence, to which
term we are now endeavouring to attach a definite connotation.
Our definition of rejuvenescence, karyogamic or other,
is that it is essentially a process of constitutional
invigoration, 2 as its converse, senescence, is one of constitutional
enfeeblement. We can now, grasping this idea, understand
the continued existence of agamous and apogamous forms
side by side with those where not merely karyogamy, but allogamous
sexual reproduction is essential. Every arrangement
that makes for protection and comfort tends to become by habit
indispensable,and the privation of such an "acquired need"
may produce effects none the less disastrous because it was acquired,
and not primitive. A couple of examples from human
life will illustrate this. The Maoris found scant clothing necessary
in their cool but not extreme climate until the Europeans
introduced blankets; but now their occasional reversion to the
practice of going unclothed is said to lead to disastrous results.
Civilised nations who cook their food largely escape the attacks
of entozoa : but, on the other hand, when they do occur,
these attacks disturb and disorder the system the more
seriously for their rarity; while the Abyssinian, who feeds
daily on raw beef, thinks it positively unlucky to be without
a tapeworm in his intestines. The coexistence of agamous,
karyogamous, and apogamous types proves that the need for
karyogamy belongs to the class of acquired needs or necessary
1 ' Vergleich der Ei,' &c, p. 85. I have not been able to consult Boveri's
original paper in the libraries of our scientific societies.
3 Of course I use " constitutional" in the medical sense.