272 RECENT CYTOLOGY 
of this division pass into different gametes. These 
latter divisions are of two kinds, since in one of them 
the heterotropic chromosome takes part, whilst in the 
other it is wanting; consequently, two out of the 
four spermatozoa eventually produced contain the 
heterotropic chromosome and two do not. (Only one 
a 
Somatic cells 
Fusion of 
Chromosomes 
& 
v 
o~ 
/, 
@ Spermatazo 
i 
+O 
oS 
Qee 
ee) 
er) 
9 DM 
x 
+ 
@ 
i} 
Fig. 47. 
ov, ovum ; #b, polar body; sp, spermatozoa (a and b the two kinds). 
spermatozoon of each kind is shown in Fig. 47.) Thus 
there is a differentiation of the spermatozoa into two 
different kinds, and one of these kinds contains a 
chromosome less than the other. On the other hand, 
every egg (as well as every polar body) contains an 
idiochromosome. 
In fertilization some of the eggs become impregnated 
