STRUCTURE AND DEVELOPMENT OF VE IITEBRATIC OVARY, 387 



by specially large ova, into the bays between which are processes 

 of the stroma. In an ovary about this stage, hardened in osmic 

 acid, the epithelium stains very differently from the subjacent 

 stroma, and the line of separation between the two isquite sharp. A 

 figure of the wdiole ovarian ridge, showing the relation between the 

 two parts, is represented on PI. XVII, fig. 5. 



The layer of stroma in immediate contact with the epithelium 

 is very different from the remainder, and appears to be destined 

 to accompany the vascular growths into the epithelium, which 

 wnll appear in the next stage. The protoplasm of the cells com- 

 posing it forms a loose reticulum with a fair number of oval or 

 rounded nuclei, with their long axis for the most part parallel to 

 the lower surface of the epithelium. It contains, even at this 

 stage, fully developed vascular channels. 



The remainder of the stroma of the ovarian ridge has now 

 acquired a definite structure, which remains constant through life, 

 and is eminently characteristic of the genital ridge of both sexes. 

 The bulk of it (PL XVII, fig. 3, sir) consists of closely packed 

 polygonal cells, of about O'OII mm. with large nuclei of about 

 U'009. These cells appear to be supjjorted by a delicate reticulum. 

 The whole tissue is highly vascular, with the numerous capillaries ; 

 the nuclei in the walls of which stand out in some preparations 

 with great clearness. 



In the next oldest ovary, of which I have sections, the breadth 

 of the ovarian epithelium is 0*7 mm. and its thickness 0"096. 

 The ovary of this age was preserved in osmic acid, which is the 

 most favorable reagent, so far as I have seen, for observing the 

 relation of the stroma and epithelium. On PI. XVII, fig. 6, 

 is represented a transverse section through the whole breadth 

 of the ovary, slightly magnified to show the general relations of the 

 parts, and on PI. XVII, fig. 7, a small portion of a section more 

 highly magnified. The inner surface of the ovarian epithelium 

 is more irregular than in the previous stage, and it may be 

 observed that the subjacent stroma is growing in amongst the 

 ova. Prom the relation of the two tissues it is fairly clear that 

 the growth which is taking ])lace is a definite growth of the 

 stroma into the epithelium, and not a mutual intergrowth of the 

 two tissues. The ingrowths of the stroma are, moreover, directed 

 towards individual ova, around which, outside the follicular 

 epithehum, they form a special vascular investment in the 

 succeeding stages. They are formed of a reticular tissue with 

 comparatively few neuclei. 



By the next stage, in my series of ovaries of Sci/. canicnla, im 

 portant changes have taken place in the constitution of ovarian 

 epithelium. Pig. 8, PI. XVII, represents a portion of the 

 ovarian epithelium, on the same scale as figs. 1, 2, 3, &c., and 



