STRUCTURE AND DEVELOPMENT OF VERTEBRATE OVARY, 429 



beautiful reticulate nuclei, with, as a rule, one more especially 

 developed nucleolus, and smaller granular bodies. Their diameter 

 varies from about 0"028 to O-O-i mm. and that of their nucleus 

 from 0'016 to 0*02 mm. The majority of these ova are not pro- 

 vided with a follicular investment, but amongst them are nume- 

 rous small cells, clearly derived from the germinal epithelium, 

 which are destined to form the follicle {vide fig. 40 a and b). In 

 a few cases the follicles are completed, and are then formed of very 

 flattened spindle-shaped (in section) cells. In the majority of 

 cases all the ova of each nest are quite distinct, and each pro- 

 vided with a delicate vitelline membrane (fig. 40 a). In other 

 instances, which, so far as I can judge, more common than in the 

 previous stages, the protoplasm of two or more ova is fused 

 together. 



Examples of this are represented in PI. XIX^ fig. 40 a. In 

 some of these the nuclei in the undivided protoplasm are all of 

 about the same size and distinctness, and probably the protoplasm 

 eventually becomes divided up into as many ova as nuclei ; in other 

 cases, however, one or two nuclei clearly preponderate over the 

 others, and the smaller nuclei are indistinct and hazy in outline. 

 In these latter cases I have satisfied myself as completely as in the 

 case of Elasmobranchs, that only one or two ova (according to 

 the number of distinct nuclei) will develop out of the polynuclear 

 mass, and that the other nuclei atrophy, and the material of which 

 they were composed, serves as the nutriment for the ova which 

 complete their development. This does not, of course, imply that 

 the ova so formed have a value other than that of a single cell, 

 any more than the development of a single embryo out of the 

 many in one egg capsule implies that the embryo so developing 

 is a compound organism. 



In the innermost layer of the germinal epithelium the out- 

 lines of the original large nests are still visible, but many of 

 the follicles have been cut off by ingrowths of stroma. In 

 the still intact nests the formation of the follicles out of the cells 

 of the germinal epithelium may be followed with great advantage. 

 The cells of the follicle, though less columnar than was the case 

 at an earlier period, are more so than in the case of follicles formed 

 in the succeeding stages. The previous inequality in the cells of 

 the follicles is no longer present. 



The tubuliferous tissue in the zona vasculosa appears to me 

 to have rather increased in quantity than the reverse ; and 

 is formed of numerous solid columns or oval masses of cells, 

 separated by strands of connective tissue, with typical spindle 

 nuclei. 



It is partially intelligible to me how Dr. Foulis might from 

 an examination of the stages similar to this, conclude that the 



