142 TUANSACTIONS AND PUOCEEDINGS OF THK [Sess. Lxvi. 



The publication of the present writing has been delayed 

 for several months, in order that time might be gained for 

 the tabulation and counting of the primary germ-cells in a 

 series of embryos. This has now (March 1901) been done 

 in eighteen embryos of Eaja hatis, and in eight of Scyllium 

 canicula. 



The number of primary germ-cells in the embryology of 

 Baja hatis may be taken at 256 in the male, and 512 in 

 the female. It may be added that the number appears to 

 be much smaller in Rana esciilenta, and in Petromyzon 

 planeri. In the former eight, and in the latter thirty-two, 

 primary germ-cells would seem to arise. These latter 

 numbers have not yet been confirmed on a material large 

 enough to afford any certainty of their correctness. 



The division of the primitive germ-cell into primary 

 germ-cells is a well-marked epoch in the life-cycle, and 

 one of the greatest possible moment. Hitherto its import 

 has been overlooked by every embryologist, and the record 

 of it is now made for the first time as the result of my 

 work. 



From every point of view it is as important as the 

 phenomena of maturation ; and probably its essential ne- 

 cessity in development will not need to wait long for 

 ample recognition. 



The number of the products of the primitive germ-cell 

 is very large in the skate — as many as 512. But it must 

 be pointed out that this number furnishes no criterion for 

 other animals. There may be cases in which it is larger, 

 though, I imagine, the occurrence of many such is un- 

 likely. Undoubtedly there are instances in which it is 

 much smaller ; and probably these are well represented 

 among the Invertebrata. In short, it may be as low as 

 two ; but as the sexual generation or embryo must arise 

 from one product, and as this must contain some sexual 

 elements, it can never be lower than two. In other words, 

 the primitive germ-cell must divide at least once, yielding 

 two primary germ- cells, of which one will give rise to the 

 embryo, and the other will supply the " sexual products." 

 Apparently it divides once in Ci/elops and Ascaris niegalo- 

 cephala, twice in Cecidomyia, and thrice in Chironomus. 



In other chapters of my work, the essential similarity 



