OF THE VERTEBRATE OVARY. 553 



will 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 (PI. 24, fig. 3, sfr) consists of closely 

 packed polygonal cells, of about 0*014 mm - with large nuclei of 

 about 0-009. These cells appear to be supported 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 07 mm. and its thickness 

 0-096. The ovary of this age was preserved in osmic acid, which 

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

 the relation of the stroma and epithelium. On PI. 24, fig. 6, is 

 represented a transverse section through the whole breadth of 

 the ovary, slightly magnified to shew the general relations of 

 the parts, and on PI. 24, 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. From the relation of the two tissues it is fairly clear that 

 the growth which is taking place 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 epithelium, they form a special vascular investment in 

 the succeeding stages. They are formed of a reticular tissue 

 with comparatively few nuclei. 



By the next stage, in my series of ovaries of Scy. canicnla, 

 important changes have taken place in the constitution of 

 ovarian epithelium. Fig. 8, PI. 24, represents a portion of the 

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

 fig. 9 a section through the whole ovarian ridge slightly magni- 

 fied. Its breadth is now 1*3 mm., and its thickness 03 mm. 

 B. 36 



