STRITCrritE AND DEVELOPMENT OF VERTliBRATE OVARY. 385 



\rhich I believe to be new, and, perhaps, of some little interest ; 

 they differ, moreover, in many iin])ortant particulars, both as to 

 the structure and development of the ovary from the accounts of 

 my predecessors. 



The history of the female generative organs may conveniently 

 be treated under two heads, viz. (1) the history of the ovarian 

 ridge itself, and (2) the history of tlie ova situated in it. I pro- 

 pose dealing in the first place with the ovarian ridge. 



The Ovarian ridge in ScylUum. — At the stage spoken of in my 

 ^HMMigraph on Elasinobranch Fishes as stage L, the ovarian ridge 

 has a very small development, and its maximum height is about 

 0*1 mm. It exhibits in section a somewhat rounded form, and is 

 slightly constricted along the line of attachment. It presents two 

 surfaces, which are respectively outer and inner, and is formed 

 of a layer of somewhat thickened germinal epithelium separated 

 by a basement membrane from a central core of stroma. The 

 epithelium is far thicker on the outer surface than on the inner, 

 and the primitive ova are entirely confined to the former. The 

 cells of the germinal epithelium are irre2;ularly scattered around 

 the primitive ova, and have not the definite arrangement usually 

 characteristic of -epithelial cells. Each of them has a large 

 nucleus, with a deeply staining small nucleolus, and a very scantv 

 protoplasm. In stage N the ovarian ridge has a pointed edge and 

 narrower attachment ihan in stage l. Its greatest height is 

 about 017 mm. There is more stroma, an 1 the basement mem- 

 brane is more distinct than before ; in other respects no changes 

 worth recording have taken place. By stage p a distinction is 

 observable between right and left ovarian ridges ; the right one 

 has, in fact, grown more rapidly than the left, and the difference 

 in size between the two ridges becomes more and more con- 

 spicuous during the succeeding stages, till the left one ceases to 

 grow any larger, though it remains for a great part of life as a 

 small rudiment. 



The right ovarian ridge, which will henceforth alone engage 

 our attention, has grown very considerably. Its height is now 

 about 0-4 mm. It has in section (e;?'</£; PI. XVII, fig. 1) a triangular 

 form with constricted base, and is covered by a flat epithelium, 

 except for an area on the outer surface, in length co-extensive 

 with the ovarian ridge, and with a maximum breadth of about 

 0'25 mm. This area will be spoken of as the ovarian area or 

 region, since the primitive ova are confined to it. The epithelium 

 covering it has a maximum thickness of about 0'05 mm., and thins 

 off rather rapidly on both borders, to become continuous with the 

 general epithelium of the ovarian ridge. Its cells have the same 

 character as before, and are several layers deep. Scattered 

 irregularly amongst them are the primitive ova. The germinal 



