660 The American Naturalist. [August, 
to develop by admitting a spermatozoan which fertilized the denu- 
cleated ovum and produced a complete individual ! 
In opposing the vitalizing properties of the sperm, Weis- 
mann, however, went further, and advocated the view that 
there is nothing in the nature of vitalization or “rejuvenes- 
cence” in conjugation—that, given proper environment, pro- 
toplasm is immortal, and runs upon a course of undiminished 
activity. This we have seen is not the case in the Infusoria, 
and, as recently remarked by Hartog, there is only one class 
of organisms which, according to our present knowledge, are 
completely agamous and immortal—namely, the Monadina. 
It may in future appear that even in the monads there is a 
cycle for the development in which conjugation plays its part. 
Maupas’s experiments seem to establish the primitive, and 
therefore the true, interpretation of the purpose of conjugation 
as well as of sex, the latter being a consequence of the former, 
namely, that after a long period of direct subdivision of her- 
editary material from a single individual, a limit is reached 
beyond which the forces of heredity are not reproduced in 
their original intensity unless combined with another set of 
similar forces of different origin. This combination restores 
the original intensity. It is objected to this that two sets of 
feeble forces cannot constitute one vigorous force, but this is 
met by the observed fact that such union does start a new life 
cycle, and is therefore rejuvenescent. We may regard this as 
the fundamental meaning of conjugation and the production 
of variations as entirely secondary. 
The Distribution of the Chromatin—We have now reviewed 
some of the main phenomena of fertilization; there still 
remains the relation of the hereditary substance to the future 
development of the individual. There is, first, the astonishing 
fact that, as the chromatin goes on dividing, its mass or vol- 
ume remains apparently undiminished ; that is, there is appar- 
ently as much chromatin in one of the many million active 
cells of the body as in the original fertilized ovum, and there 
is still an enigma as to the nature of this chromatin and its — 
functions. Secondly, there is the problem of the maternal and 
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