1887] The Significance of Sex. A 229 
be a fusion of nuclei to a greater or a less extent before spore 
multiplication; and the same thing happens with multinucleated 
forms like Gastrostyla, Actinophrys, and Actinospherium. Multi- 
nucleated cells are not separated from plasmodia by any distinct 
line, for in Heliozoa, Greeff found that division of the cell is facul- 
tative and optional, following the nuclear division, and if it occurs, 
the cell-bodies are apt to fuse again. In low forms of Protozoa 
conjugation also is as facultative as with those protophyta, where 
both male and female parthenogenesis have been noticed. 
We may get conjugation between ordinary zooids, or one of 
the gametes may be a microgonidium while the other, not having 
divided so fast, remains as a macrogonidium. Again, the gametes 
may be due to spore formation; and here, again, the spores may 
be alike or unlike, and conjugation may be between like spores, 
or may be between macrospores and microspores. If the con- 
ditions of life are equal, the more often the cell-division has 
taken place the stronger is the desire and need of conjugation, so 
that where macrospores are parthenogenetic, microspores may be 
gametes. That this need of conjugation does not depend on the 
small quantity of idioplasm present may be gathered from two 
facts : first, when spore formation succeeds conjugation the re- 
sulting spores are smaller and more numerous than if parthen- 
ogenetically produced, but whereas the latter are apt to be 
gametes the former grow with vigor and multiply rapidly; 
secondly, where cell-multiplication allows time for the cell to 
grow as in ordinary gonidia, gametes are just as apt to form. In 
spore formation the microspores are not gametes more often than 
the macrospores because they are small, but because they have 
undergone division more frequently. In forms where both 
gonidial and sporular gametes occur, a failure to conjugate in 
_ the gonidial stage insures conjugation of the spores, while the 
occurrence of conjugation in the gonidial stage insures sporular 
parthenogenesis. 
The Vorticellz enable us to understand that fertilization has to 
do with quality of the gemmules and not with the number of 
these present. Two zooids which have resulted from the repeated 
division of a mother-zygote and standing near each other bend 
together and conjugate. But others just like these bud off a 
piece off the nucleus with some of the cytoplasm, and this goes 
swimming away until it finds the appropriate gamete (a macro- 
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