MUSEUM OF COMPAEATIVE ZOOLOGY. 135 



granulosa is torn from the egg membranes, as, owing to the shrinkage of 

 the egg, it frequently is, the processes no longer show the same sharp 

 outer margins. Their edges are often frayed, and are not stained as 

 deeply as when the granulosa and the membranes are in their normal 

 relations to each other. With the separation of the granulosa the thin 

 outer membrane is sometimes torn (Fig. 15 a ); and whether torn or 

 not, it is often separated from the inner membrane. This may be due 

 to the fact that the processes are from the beginning adhesive, and 

 have thus acquired an intimate secondary relation to the cells of the 

 granulosa. In such sections it can be clearly seen that the rivet-shaped 

 processes are joined to the outer membrane and not to the zona, though 

 their bases have projected into the zona for a greater or less distance. 

 When the granulosa is torn from the egg membranes, the processes 

 always, even in the smallest eggs, remain attached to the membranes 

 rather than to the granulosa. I have been able to find neither the 

 nuclear structure within nor the prolongations from these processes 

 which Owsjannikow has described. 



I have not succeeded in finding the micropyle in eggs that were much 

 less than 0.4 mm. in diameter; in such the zona has an average thick- 

 ness of about 5 jx. The portion immediately surrounding the micro- 

 pyle shows a considerable local thickening. Owing to the variation in 

 the thickness of the zona in different regions of the same egg, and to the 

 inconstancy of the position of the micropyle in relation to this varia- 

 tion, it sometimes happens that the zona at the micropylar region has 

 already reached a thickness of 10 or 11 /x. 



It is a noticeable fact, that at this earlier stage the micropyles of 

 nearly all the eggs were cut radially when the sections were made 

 in planes perpendicular to the axis of the ovary. Furthermore, the 

 micropyles uniformly lie in the half of the egg opposite the side of 

 attachment. 



In the vicinity of the micropyle the zona becomes thickened by the 

 elevation of its outer surface, the deeper surface undergoing no change of 

 direction. At a distance of about 10 yu, on either side of the micropylar 

 canal it attains its greatest thickness, and then its outer contour curves 

 inward until it becomes continuous with the wall of the micropylar 

 canal. The inner end of the canal is sometimes slightly enlarged 

 (Figs, 19-22). 



At this stage the pore canals of the zona radiata do not seem to be 

 modified in direction in the region of the micropyle ; they are all 

 radially arranged. The outer membrane could not be distinguished in 



