THE DEVELOPMENT OE THE MOLE. 209 



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. 



The 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 difi"erence at all, as is practically the 

 case in the ovum figured (fig. 11), the one segment being 

 30-35 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. 213. 



