400 Experimental Zovlogy 
pole and the other half to the other pole, and the second polar 
body is formed (Fig. 6). Thus while the first division is a déj- 
jerential division, the second is an equation division. It is 
supposed, also, that in some eggs the above order is reversed, 
and the first division is an equation division, and the second 
a differential one. The end result is the same in both 
cases. 
An exactly parallel series of events takes place in the formation 
of the spermatozoén. The early sperm-cells, the spermato- 
gonia, contain the full number of chromosomes. These pair, as 
in the egg, and two cell divisions take place later, — one a differ- 
ential, and the other an equation division. In the case of the 
sperm-cells, however, all four cells become functional sperma- 
tozoa, while-in the egg the polar bodies do not develop. The 
first polar body often divides. The three polar bodies and the 
egg are equivalent to the four spermatozoa. 
What support do these results give to the hypothesis that sex 
is determined at one or at both of these divisions? The facts 
so far stated furnish no real support for this idea, since the 
differential division merely separates a paternal from a maternal 
chromosome; and if we do not confuse paternal with male pro- 
ducing, and maternal with female producing, there is nothing in 
the facts, as I have said, that supports the idea that this division 
is a sex-determining one. In regard to the equation division, 
the observations show that the chromosomes split into exactly 
like halves, and there is also nothing here to support the idca 
that one half is male and the other half female determining, 
for this division resembles, outwardly at least, all other equation 
divisions of the body-cells that are supposed to produce equiva- 
lent parts. 
If this were the only evidence we possessed in regard to the 
maturation divisions, it would lend no support to the hypothesis 
that the sex of the egg or of the sperm is determined at this time; 
but there are some recent observations showing that in a few 
_groups two kinds of spermatozoa are formed, so far as their 
chromosomal contents is concerned, and we must now examine 
