432 F, M. BALFOUK. 



composed of branclied 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 becomes 

 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 trabeculse) may be spoken of as nests. In 

 the course of the development of the ova they are broken op 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, Rep- 

 tiles, &c., with numerous primitive ova embedded amongst the 

 small cells of the germinal epithelium, are not found. 



(4) The conversion of the cells of the germinal epithelium 

 into permanent ova commences in an embryo of about twenty- 

 two days. All the cells of the germinal epithelium appear to 

 be capable of becoming ova : the following are the stages in 

 the process, which are almost identical with those in Elasmo- 

 branchs : — 



(a) The nucleus of the cells loses its more or less distinct net- 

 work, and becomes very granular, with a few specially large 

 granules (nucleoli). The protoplasm around it becomes clear 

 and abundant — primitive ovum stage. It may be noted that 

 the largest primitive ova are very often situated in the pseudo- 

 epithelium, (d) A segregation takes place in the contents of the 

 nucleus within the membrane, and the granular contents pass 

 to one side, where they form an irregular mass, while the re- 

 maining space within the membrane is perfectly clear. The 

 granular mass gradually develops itself into a beautiful reticulum, 

 with two or three highly refracting nucleoli, one of which eventu- 

 ally becomes the largest and forms the germinal spot par 

 excellence. At the same time the body of the ovum becomes 

 slightly granular. While the above changes, more especially 



