THE DEVELOPMENT OF THE MOLE. 165 
closely surrounded by the vitelline membrane. The circum- 
vitelline space is narrow, and within this space a number of 
spermatozoa and also two polar bodies were observed. The 
ovum appears to have expanded considerably since the matura- 
tion stage when the circum-vitelline space was wide, for in the 
ovum represented in the figure the polar bodies are greater in 
diameter than is this space, and thus cause a depression on the 
surface of the ovum. 
As to the number of spermatozoa which actually enter the 
substance of the ovum I have no more evidence than appears 
in the drawing (fig. 10), in which if my interpretations are 
correct, a single male pronucleus is present. No movement 
was observed among the spermatozoa within the peri-vitelline 
space; they appear to be attached there, and indeed in the 
case of a similarly-conditioned ovum when the zona was 
removed, these spermatozoa remained fixed to the vitellus and 
were not pulled away with the zona. 
I have always failed to observe either the presence of cilia 
or a rotation of the ovum within the zona such as Bischoff 
describes. 
Tur SEGMENTATION. 
The first segmentation furrow gives rise to two oval seg- 
ments of which one is generally somewhat larger than the 
other, although the difference in size may be quite inconsider- 
able, or there may be no difference at all, as is practically the 
case in the ovum figured (fig. 11), the one segment being 
20°25 x 15°5, the other 19°75 x 16. 
The vitellus in both segments is finely granular and presents 
no difference in character in either segment. 
The nuclei are distinct, numerous spermatozoa are contained 
within the circum-vitelline space, and two polar bodies are 
visible. 
The zona radiata, with its rough granular outer border, is 
distinctly striated. 
The measurements of the segments of several other ova of 
this stage are given in the table on p. 169. 
