THE URINOGENITAL SYSTEM. 353 



In the particular embryo whose primitive ova have been 

 described these bodies were more conspicuous than in the 

 majority of cases, but at the same time they presented no 

 special or peculiar characters. 



In a somewhat older embryo of Scyllium the cells amongst 

 which the primitive ova lay had become very distinctly dif- 

 ferentiated as an epithelium (the germinal epithelium of 

 Waldeyer) well separated by what might almost be called a 

 basement membrane from the adjoining connective-tissue cells. 

 Hardly any indication of a germinal ridge had appeared, but 

 the ova were more definitely confined than in previous embryos 

 to the restricted area which eventually forms this. The ova on 

 the average were somewhat smaller than in the previous cases. 



In several embryos intermediate in age between the embryo 

 whose primitive ova were described at the commencement of 

 this section and the embryo last described, the primitive ova 

 presented some peculiarities, about the meaning of which I am 

 not quite clear, but which may perhaps throw some light on the 

 origin of these bodies. 



Instead of the protoplasm around the nucleus being clear or 

 slightly granular, as in the cases just described, it was filled in 

 the most typical instances with numerous highly refracting 

 bodies resembling yolk-spherules. In osmic acid specimens (PL 

 12, fig. 15) these stain very darkly, and it is then as a rule very 

 difficult to see the nucleus; in specimens hardened in picric 

 acid and stained with hsematoxylin these bodies are stained of a 

 deep purple colour, but the nucleus can in most cases be dis- 

 tinctly seen. In addition to the instances in which the proto- 

 plasm of the ova is quite filled with these bodies, there are 

 others in which they only occupy a small area adjoining the 

 nucleus (PL 12, fig. 15 a), and finally some in which only one or 

 two of these bodies are present. The protoplasm of the 

 primitive ova appears in fact to present a series of gradations 

 between a state in which it is completely filled with highly 

 refracting spherules and one in which these are completely 

 absent. 



This state of things naturally leads to the view that the 

 primitive ova, when they are first formed, are filled with these 

 spherules, which are probably yolk-spherules, but that they 



