146 



I. IKEDA. 



It is henceforth necessary to treat of the ovary and the testis sepa- 

 rately. I will take up the former first, as giving a clearer insigbt into 

 the developmental process. 



The Ovary and Its Product. — Closely following their first formation, 

 the oogonia begin to differentiate themselves into the oocytes and the 

 follicular cells, the two kinds of cells which go to form the entire ovarian 

 tissue. The former are distinguished by the larger size, which of course 

 beccmes more and more pronounced with the advance in growth ; the 

 latter remain small and are arranged around and between the former- 

 Each egg-follicle thus consists of a central oocyte enveloped in a single- 

 layered follicular epithelium. Around and along the capillary the follicles 

 range themselves in a layer. They show amongst them a considerable 

 difference in size from an early period of their development. A definite 

 rule seems not to exist as to the relative situation of the largest and the 

 smallest follicles, though at a later stage of the ovarian development it 

 is often noticeable that those more proximally situated on a capillar}' 

 are on the whole the more advanced in growth. 



As already indicated, the ovarian tissue is at first covered over by 

 the nutriment layer. In inverse proportion as the follicles or the oocytes 

 in that tissue grow in size, the overlying nutriment cells diminish in 

 height (see PL.V., figs. 2 and 3) ; that is to say, they become smaller and 

 smaller, while the inclosed yolk-like spheres constantly diminish in quan- 

 tity. The smallest and simple spheres are the first that disappear, evi- 

 dently as the result of resorption. This leads finally to the total dis- 

 appearance of the spheres as well as of the nutriment cells themselves, 

 after which the ovarian tissue forms the outermost layer of the capillary 

 wall and is thus directly washed by the ccelomic fluid (fig. 4). It may be 

 said in general that as the development of the ovarian tissue advances, 

 starting from the capillary base, the nutriment layer gradually dwindles 

 awcy before it. 



Ala certain stage in the genesis of the ovary, the numerous capil- 

 laries giving foundation to it may show the transformation carried out to 

 various degrees. While some capillaries or capil'ary branches may 



