OVARIAN STRUCTURES OF VIVIPAROUS BLIND FISHES. 45 



development, there being always a more or less marked differ- 

 ence in size. 



Between the ovisac and the ovary proper there is a lumen of 

 varying size. When there are larvae present, the ovisac and the 

 oviduct are extremely thin and so stretched, especially near the 

 close of gestation, that their cellular structure cannot be made 

 out with any satisfaction (Fig. 5). Shortly after birth of the 

 young they contract and assume the form and appearance found 

 in the ovaries of mature but non-pregnant females (Fig. 3). The 

 wall of the ovisac is then quite thick, and the lumen very small. 

 The histological structure of the ovisac will be described below. 



In non-pregnant ovaries, the stroma is a mass, which, in- 

 ternally, has a bilateral arrangement and occupies most of the 

 space within the ovisac (Figs. 2, 3). It is, in general shape, 

 fusiform with its largest diameter just posterior to the division 

 of the ovisac into the two horns down both of which it is con- 

 tinued along their median surfaces, forming the prongs of a Y. 

 In the middle of the ovary the stroma forms a median parti- 

 tion ; somewhat posteriorly this partition is cut across (Fig. 3), 

 and still further back only the ventral part remains (Fig. 2). 

 It has many lobes which are usually somewhat pointed and 

 comparatively large and distinct, the indentations sometimes leav- 

 ing merely a "neck" of tissue to support them. The whole 

 stroma at this time is fully distended by the large amount of lymph 

 contained in the sinuses described below. Where the ova are well 

 advanced they can be seen by the unaided eye in the form of 

 opaque dots. When the ova are surrounded by follicles, they 

 lie some distance below the surface of the stroma and there is 

 a tubular indentation of the epithelial covering of the latter down 

 to the follicle (Fig. 7, /?). In a circular space over the egg the 

 epithelium is apparently continuous with the follicle. It is only 

 on very close inspection that the independence of the follicle can 

 be made out. It is then found to be of only a single cell in thick- 

 ness beneath the epithelial indentation. A similar position of the 

 epithelium was noted by Stuhlmann over the ova in the ovary 

 of Zoarccs and was called " Delle " by him. 



The pregnant ovary is quite different in appearance from that 

 of a non -pregnant female. A cross-section of the former shows 



