606 THE STRUCTURE AND DEVELOPMENT 



later and independent formation, but am inclined myself to 

 adopt the latter view. The first formed membrane, whether or 

 no it becomes the zona radiata, is very similar to the vitelline 

 membrane of Elasmobranchs and arises at a corresponding stage. 



Summary of observations an tfie mammalian ovary. The 

 general results of my observations on the mammalian ovary are 

 the following : 



(1) The ovary in an eighteen days' embryo consists of a 

 cylindrical ridge attached along the inner side of the Wolffian 

 body, which is formed of two parts ; (a) an external epithelium 

 two or three cells deep (the germinal epithelium); (b) a hilus 

 or part forming in the adult the vascular zone, at this stage 

 composed of branched masses of epithelial tissue (tubuliferous 

 tissue) derived from the walls of the anterior Malpighian bodies, 

 and numerous blood-vessels, and some stroma cells. 



(2) The germinal epithelium gradually becomes thicker, 

 and after a certain stage (twenty-three days) there grow into it 

 numerous stroma ingrowths, accompanied by blood-vessels. The 

 germinal epithelium thus becomes honeycombed by strands of 

 stroma. Part of the stroma eventually forms a layer "close below 

 the surface, which becomes in the adult the tunica albuginea. 

 The part of the germinal epithelium external to this layer be- 

 comes reduced to a single row of cells, and forms what has been 

 spoken of in this paper as the pseudo-epithelium of the ovary. 

 The greater part of the germinal epithelium is situated internal 

 to the tunica albuginea, and this part is at first divided up by 

 strands of stroma into smaller divisions externally, and larger 

 ones internally. These masses of germinal epithelium (probably 

 sections of branched trabeculae) may be spoken of as nests. In 

 the course of the development of the ova they are broken up by 

 stroma ingrowths, and each follicle with its enclosed ovum is 

 eventually isolated by a layer of stroma. 



(3) The cells of the germinal epithelium give rise both to 

 the permanent ova and to the cells of the follicular epithelium. 

 For a long time, however, the cells remain indifferent, so that 

 the stages, like those in Elasmobranchs, Osseous Fish, Birds, 

 Reptiles, &c., with numerous primitive ova embedded amongst 

 the small cells of the germinal epithelium, are not found. 



