OF THE VERTEBRATE OVARY. 6OI 



factory proof that the follicular epithelium takes its origin-from 

 the germinal epithelium and not from the stroma or tubuliferous 

 tissue. The several categories of elements observable in such a 

 nest deserve a careful description. 



(1) The large ova in their follicles. These ova have 

 precisely the character of the young ova in Elasmobranchs. 

 They are provided with a granular body invested by a delicate, 

 though distinct membrane. Their nucleus is large and clear, 

 but traversed by the network so fully described for Elasmo- 

 branchs. The cells of their follicular epithelium have obviously 

 the same character as many other small cells of the nest. Two 

 points about them deserve notice (a) that many of them 

 are fairly columnar. This is characteristic only of the first 

 formed follicles. In the later formed follicles the cells are 

 always flat and spindle-shaped in section. In this difference 

 between the early and late formed follicles Mammals agree with 

 Elasmobranchs. (b] The cells of the follicle are much more 

 columnar towards the inner side than towards the outer. This 

 point also is common to Mammals and Elasmobranchs. 



Round the completed follicle a very delicate membrana pro- 

 pria folliculi appears to be present 1 . 



The larger ova, with follicular epithelium, measure about 

 0*04 mm., and their nucleus about O'O2 mm., the smaller ones 

 about o - O22 mm., and their nucleus about 0*014 mm. 



(2) Medium sized ova. They are still without a trace of a 

 follicular epithelium, and present no special peculiarities. 



(3) The smaller cells with modified nuclei. I have great 

 doubt as to what is the eventual fate of these cells. There ap- 

 pear to be three possibilities. 



(a) That they become cells of the follicular epithelium ; (ft) 

 that they develop into ova ; (c) that they are absorbed as a kind 

 of food by the developing ova. I am inclined to think that 

 some of these cells may have each of the above-mentioned des- 

 tinations. 



(4) The cells which form the follicle. The only point to be 

 noticed about these is that they are smaller than the indifferent 



1 Loc. cit., Waldeyer, p. 23, denies the existence of this membrane for Mam- 

 malia. It certainly is not so conspicuous as in some other types, but appears to me 



nevertheless to be always present. 



!' 39 



