STRUCTURE AND DEVELOPMEXT OF VERTEBRATE OVARY. 433 



those in th€ nucleus, have been taking ])]ace, the protoplisni 

 of two or more ova may fuse together, and polynuclear masses 

 be so formed. In some cases the whole of such a poljnuclear 

 mass gives rise to only a single ovum, owing to the atrophy of all 

 the nuclei but one, in others it gives rise by subsequent division 

 to two or more ova, each with a single germinal vesicle. 



(5) All the cells of a nest do not undergo the above changes, 

 but some of them become smaller (by division) than the indif- 

 ferent cells of the germinal epithelium, arrange tliemselves round 

 the ova, and form the follicular epithelium. 



(6) Tlie first membrane formed round the ovum arises in 

 some cases even before the appearance of the follicular epithelium, 

 and is of the nature of a viteihne membrane. It seems probable, 

 although not definitely established by observation, that the zona 

 radiata is formed internally to the vitelline membrane, and that 

 the latter remains as a membrane, somewhat irregular on its outer 

 border, against which the ends of the follicle cells abut. 



General Observations on the Siuucture and Development 

 OF THE Ovary. 



In selecting Mammalia and Elasmobranchii as my two 

 types for investigation, I had in view the consideration that 

 what held good for such dissimilar forms might probably be ac- 

 cej)ted as true for all Vertebrata with the exception of Amphioxus. 



The structure of the ovary. — From my study of these two 

 types, I have been led to a view of the structure of the ovary, 

 which differs to a not inconsiderable extent from that usually en- 

 tertained. For both types the conclusion has been arrived at 

 that the whole egg-containing part of the ovary is really the 

 thickened germinal epithelium, and that it differs from the 

 original thickened patch or layer of germinal epithelium, mainly 

 in the fact that it is broken up into a kind of meshwork by 

 growths of vascular stroma. If the above view be accepted 

 for Elasmobranchii and Mammalia, it will hardly be disputed for 

 the ovaries of Ileptilia and Aves. In the case also of Osseous 

 Fish and Amphibia, this view of the ovary appears to be very 

 tenable, but the central core of stroma present in the other types 

 is nearly or quite absent, and the ovary is entirely formed of the 

 germinal epithelium with the usual strands of vascular stroma.^ 

 It is obvious that according to the above view Pfliiger's egg- 

 tubes are merely trabeculse of germinal epithelium, and have 

 no such importance as has been attributed to them. They 

 are present in a more or less modified form in all types of 



%■- '"My view of the structure of tlu; ovary would seem to be that held bj 

 Gotte, ' Entwicklungsgeschichte d. Unke,' p. 14 and 15, 



