608 THE STRUCTURE AND DEVELOPMENT 



GENERAL OBSERVATIONS ON THE STRUCTURE 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 

 accepted as true for all Vertebrata with the exception of Am- 

 phioxus. 



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 

 entertained. 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 Elasmo- 

 branchii and Mammalia, it will hardly be disputed for the 

 ovaries of Reptilia 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 1 . 

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

 tubes are merely trabeculs 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 ovaries. 

 Even in the adult Amphibian ovary, columns of cells of the 

 germinal epithelium, some indifferent, others already converted 

 into ova, are present, and, as has been pointed out by Hertwig 2 , 

 represent Pfliiger's egg-tubes. 



The formation of tJie permanent ova. The passage of primi- 

 tive ova into permanent ova is the part of my investigation to 

 which the greatest attention was paid, and the results arrived at 

 for Mammalia and Elasmobranchii are almost identical. Al- 



1 My view of the structure of the ovary would seem to be that held by Gotte, 

 Entwicklungsgeschichte d. Unke, pp. 14 and 15. 



2 Loc. cit. 36. 



