226 The Significance of Sex. [ March 
the egg, and in many animals it is only the head of the sperma- 
tozoon that makes the male pronucleus, the greater part of the 
flagellum not even getting into the yelk, so that we are justified 
in believing that fertilization is essentially a phenomenon of the 
mixture of chromatins. e cannot speak even of the union of 
“half nuclei” to make a whole nucleus, nor say that the nuclei 
are morphologically alike, nor yet that they are the complements 
of each other in any way. That the sexual pronuclei are physio- 
logically alike we may infer from the fact that the characters of 
both parents are equally well transmitted, and from the fact that 
we may get both male and female parthenogenesis, which latter 
statement receives its best support from the evidence afforded 
by polyspermy and by the behavior of unfertilized eggs. We 
know that, aside from differences in size or in locomotor organs 
and other secondary characters, gamete may differ physiologi- 
cally in this way: in one, which we usually call the male, or mi- 
crogamete, there has been a greater number of cell-divisions than 
in the female gamete, but in the latter we may, by enforced par- 
thenogenesis, secure just as many divisions, and so make the 
cells alike. But neither of the gametes have divided as many 
times as they can, for it is possible, though more difficult than 
with the ovum, to get male parthenogenesis. The offspring 
thus resulting are more sexed, have greater desire as well as 
need for fusion with other cells, especially cells that have not 
divided as much as themselves. Unless we give such cells easy 
conditions of life we reach a stage when they can no longer 
divide. Such facts as these, observed with spores and the proto- 
organisms, enable us to understand certain phenomena obtaining 
with fertilization in higher forms of life. 
We should expect that in most cases the ovum would possess 
a tendency to segmentation, which is realized normally under con- 
ditions of easy nutrition in parthenogenetic development, but may 
be realized in a less degree with other eggs. As a matter of 
fact there have been a number of observations in widely different 
groups of animals that show a sort of irregular segmentation of 
unfertilized eggs. I have observed such cases not infrequently. 
Such segmentation is slow and irregular, and probably cannot pro- 
_ ceed as far as normal is. Pane phat nsieecteasie = a 
