5/6 THE STRUCTURE AND DEVELOPMENT 



My observations in Raja are not so full as those upon Scyllium, 

 but they serve to complete and reconcile the observations of 

 Semper and Schultz, and also to shew that the general mode of 

 growth of the follicular epithelium is fundamentally the same 

 in my representatives of the two divisions of the Elasmobranchii. 

 In very young eggs, in conformity with the results of all previous 

 observers, I find the follicular epithelium approximately uniform. 

 The cells are flat, but extended so as to appear of an unexpected 

 size in views of the surface of the follicle. This condition does 

 not, however, last very long. A certain number of the cells 

 enlarge considerably, others remaining smaller and flat. The 

 differences between the larger and the smaller cells are more 

 conspicuous in sections than in surface views, and though the 

 distribution of the cells is somewhat irregular, it may still be 

 predicted as an almost invariable rule that the smaller cells of 

 the follicle will line that part of the surface of the ovum, near to 

 which the germinal vesicle is situated. On PI. 25, fig. 30, is 

 shewn in section a fairly average arrangement of the follicle 

 cells. Semper considers the larger cells of such a follicle to be 

 probably primitive ova destined to become permanent ova. This 

 view I cannot accept : firstly, because these cells only agree with 

 primitive ova in being exceptionally large the character of 

 their nucleus, with its large nucleolus, being not very like that of 

 a primitive ovum. Secondly, because they shade into ordinary 

 cells of the follicle ; and thirdly, because no evidence of their 

 becoming ova has come before me, but rather the reverse, in 

 that it seems probable that they have a definite function con- 

 nected with the nutrition of the egg. To this point I shall 

 return. 



In the next stage the small cells have become still smaller. 

 They are columnar, and are wedged in between the larger ones. 

 No great regularity in distribution is as yet attained (PI. 25, 

 fig. 31;. Such a regularity appears in a later stage (PI. 25, fig. 

 32), which clearly corresponds with fig. 8 on PI. 34 of Schultz's 

 paper, and also with the stage of Scyllium in PL 25, fig. 29, 

 though the distinction between the two kinds of cells is here far 

 better marked than in Scyllium. The big cells have now be- 

 come flask-shaped like those in Scyllium, and send a process 

 down to the vitelline membrane. The smaller cells are arranged 



