BANCROFT: OVOGENESIS IN DISTAPLIA OCCIDENTALIS. 101 



yolk bodies; while the nucleolus remains behind (DavidofiTs Figures 

 18, 19, Taf. v.). It will be seen, however, that this condition is 

 exactly what I have found in the two abnormal ova mentioned above. 

 It may be that this appearance is more common in the species studied 

 by DavidofF than in the one with which I am familiar, and this stage 

 may possibly have some place in the normal series of events in that 

 species, but the close similarity of his other stages to mine does not 

 favor this view. 



Davidoff's ergoplasm that in some stages surrounds what he takes to 

 be the nucleolus, but finally penetrates between all the yolk bodies, is, 

 I think, the central clump of yolk surrounding the germinative vesicle 

 in class three. When stained faintly, it sometimes looks slightly 

 granular. But so far as the penetration of the yolk by this substance 

 is concerned, I cannot confirm his results; for in the later stages, as in 

 the earlier, I find no interstitial substance whatever between the yolk 

 bodies. 



The body that Davidoff takes to be the nucleolus in the later stages 

 is undoubtedly the shrunken germinative vesicle. In size, shape, and 

 in all other respects, the two objects are entirely similar. Curiously 

 enough Davidoff follows quite a number of these stages backwards, in 

 spite of the fact that he thinks that his " nucleolus " is shrinking, and 

 that his figures show the size of that structure to be increasing in the 

 successive stages. The central body which he finds developed within 

 his nucleolus is nothing but the true nucleolus of the vesicle, which I 

 have traced through all the stages, but which would often be obscured 

 by the stain he used. His main trouble consists in not having had 

 before him any of the first stages in the shrinking of the vesicle when 

 its membrane and nucleolus are easily seen. On this account also 

 he missed the entire process of the transformation of the cytoplasmic 

 reticulum into yolk, which occurs at the same period. 



That this shrivelling of the germinative vesicle is closely associated 

 with the formation of the yolk, is suggested by the synchronism of the 

 two events, and it is interesting to note that the intense activity of 

 the nucleus, of which this shrinking is probably the result, begins 

 shortly after degenerative changes have commenced in the test cells. 

 It seems, then, that the test cells are particularly active in conveying 

 nourishment to the ovum in the early stages, whereas the nucleus 

 exerts its principal activity in the later stages in converting this 

 material into yolk. 



