OF THE VERTEBRATE OVARY. 585 



off from the stalk, and so from its place of origin in the super- 

 ficial epithelium, and subsequently lies freely in the stroma of 

 the ovary." 



He further explains that the separation of the follicles from 

 the epithelium takes place much earlier in Acanthias than in 

 Raja, and that the sinkings of the epithelium into the stroma 

 may have two or three branches each with a follicle. 



Semper gives very little information with reference to the 

 post-embryonic formation of ova. He expresses his agreement 

 on the whole with Ludwig, but, amongst points not mentioned 

 by Ludwig, calls attention to peculiar aggregations of primitive 

 ova in the superficial epithelium, which he regards as either 

 rudimentary testicular follicles or as nests similar to those in the 

 embryo. 



My observations on this subject do not agree very closely 

 with those either of Ludwig or Semper. The differences between 

 us partly, though not entirely, depend upon the fundamentally 

 different view we hold about the constitution of the ovary and 

 the nature of the epithelium covering it (vide pp. 555 and 556). 



In very young ovaries (PI. 24, fig. 8) nests of ova (in my 

 sense of the term) are very numerous, but though usually super- 

 ficial in position are also found in the deeper layers of the ovary. 

 They are especially concentrated in their old position, close to 

 the dorsal edge of the organ. In some instances they do not 

 present quite the same appearance as in the embryo, owing to 

 the outlines of the ova composing them being distinct, and to 

 the presence between the ova of numerous interstitial cells 

 derived from the germinal epithelium, and destined to become 

 follicular epithelium. These latter cells at first form a much 

 flatter follicular epithelium than in the embryonic periods, so 

 that the smaller adult ova have a much less columnar investment 

 than ova of the same size in the embryo. A few primitive ova 

 may still be found in a very superficial position, but occasionally 

 also in the deeper layers. I am inclined to agree with Semper 

 that some of these are freshly formed from the cells of the 

 germinal epithelium. 



In the young female with ova of about O'5 mm. nests of ova 

 are still fairly numerous. The nests are characteristic, and 

 present the various remarkable peculiarities already described 

 B. 38 



