197_ 



male embryos, and that, therefore, there must be two kinds of eggs 

 in Raja batis, but the establishment of this beyond cavil was not the 

 work of a moment. 



The actual investigation of this little point alone entailed some 

 three months of research, and, indeed, it like all my work of the past 

 few years would have required far more time and energy, even had it 

 been at all possible to get through it ^ — a moot question — had it 

 not been for the generous self-sacrificing help of another. For in- 

 valuable assistance in cutting the thousands of sections of the scores 

 of embryos I have been, and still am, indebted to my wife. 



From enumerations ^) of the germ-cells of a sufficient number of 

 potentially male and female embryos of R, batis, to be fully given 

 elsewhere, it is certain, that the number of primary germ -cells in 

 potentially male embryos approaches more or less closely 256, in fe- 

 male embryos 512. 



This find created a desire for information as to the conditions in 

 other cases. Scyllium canicula, obtained from Wales, i. e., a variety 

 distinct from the Neapolitan one, was examined. Here also aberrant 

 germ-cells were encountered, and in places similar to those already 

 recorded for Raja. Other particulars are reserved for the memoir on 

 the germ-cells. 



No. size potential sex total germ-cells 



261 circa 20 mm ? 109 



260 „ 20 „ ? 117 



182 19 „ S 95 



186 23 „ S 121 

 152 21 „ ? 126 



187 204 „ S 127 

 52 22l „ 2 123 



100 26" „ S 100 



918 i/gth = 114.75. 



Obviously, the number is the same in the male as in the female, 

 and as clearly it must be about 128. That this number is not the 

 average one of all is accounted for by the advanced ages of the em- 



1) These must be made in embryos closely bordering upon 3«) mm, 

 not younger and not much older. Therefore, they fall to be carried 

 out, before the Muellerian ducts begin to be formed. The only point, 

 by which it has been possible to distinguish the potential sexes of such 

 embryos, is that in potential females the two most anterior nephridial 

 tubules do not at any period join the segmental duct. As Semper found, 

 there are at least four in Mustelus; while, as Balfouk and Rabl record, 



