53 



every millimetre). In my collection there are many embryos of Raja 

 and other Elasmobranchs, where attempts at enumeration have utterly 

 failed owing to the thinness of the sections and the consequent in- 

 crease in the number of discs (sections) of each germ-cell. 



Table of the Distribution of germ-cells in embryos of Pristiurus. 



The study of embryos larger than 16 mm has been avoided, be- 

 cause of the danger of approaching the period of the division of the 

 original primary germ -cells into secondary ones. The actual epoch 

 has now been established in Raja and Scyllium, and thus experience 

 has been obtained of the precautions requisite, in order that secon- 

 dary germ-cells may not be tabulated as primary germ-cells. 



Of the embryos of Pristiurus under consideration 13 lie between 

 5 mm and 16 mm. For reasons given above the total number of 

 primary germ-cells found in the different embryos varies somewhat, 

 the lowest number being 100, the highest 153. The actual figures of 

 all the cases are given in the table. Between these limits the number 

 varies, and in but two embryos does the like total occur. But, as 

 even a cursory glance at the table reveals, the number oscillates on 

 each side of 127 — 128. The total for all 13 embryos is 1655, or an 

 average of about 127 for each. Evidences of the potential sexes of 

 the embryos, in view of the improbable existence of two numbers here, 

 were only looked for in three cases, of these two were potentially 



