352 
CRESSWELL SHEARER. 
few in number, and have large granular nuclei, each sur- 
rounded with a thin layer of cytoplasm. Close examination 
shows that every female cell has been joined by a sperma- 
tozoon. The different parts of these, the heads and tails, 
can be clearly distinguished. There are apparently many 
more sperm than female cells, so that the ovary contains 
many lying free and unattached. On making a preparation 
of another female, somewhat more advanced than the one we 
have been considering, we get the condition shown in fig. 24. 
Here the process has gone a step further, and the primitive 
oogonial cells have increased appreciably in size. There, 
attached sperm-heads are visibly undergoing absorption. 
The tails of the sperm have partially disappeared, but in 
several instances can still be distinguished. The sperm 
heads are lying within the cell wall, or are in the act of 
fusing with the nuclear wall of the oogonial cells. In a 
slightly later stage still, all the sperm heads are in the cyto- 
plasm or have definitely fused with the nuclear wall of the 
oogonia. During these stages the sperm head remains a 
compact mass of darkly staining chromatin. 
Lastly they come into definite relation with the nucleus of 
the oogonial cell, so that this consists of two separate parts, 
each with its own nuclear wall, surrounded by one main 
nuclear membrane. This condition is shown under high 
magnification in fig. 34 ; and in a later stage again in fig. 29. 
The nucleus of the primitive oogonial cell, therefore, is of a 
double character : one half, the smaller, contains the male 
substance which has been derived from the sperm head, 
while the other, the larger, contains the female. These two 
parts retain their individuality throughout the growth period. 
In all the subsequent nuclear divisions these two parts of the 
nucleus divide amitotically (figs. 16, 33, 34). In none of 
these divisions does the male or female substance form indi- 
vidual chromosomes, but each divides directly into two equal 
parts. As these masses pull apart, the chromatic substance 
seems to be drawn out into irregular digitations that give at 
certain stages a false appearance of chromosome formation. 
