55 



In the course of his researches upon the embryos of raja, 

 and as the result of his painstaking labour of enumerating the 

 primary germ-cells, he found that in every instance where it 

 was possible to make an approximately correct count, the 

 number was always either close upon 256 or 512. Further 

 research resulted in the discovery that embryos containing 

 about 256 primary germ-cells invariably gave rise to male 

 skates, while those containing about 512 gave rise to female 

 skates. Here, then, was demonstrated the existence of two 

 kinds of eggs, eggs producing males, and eggs producing females. 

 At first sight it would naturally be assumed that, in the event 

 of the 256 primary germ-cells — potential males — undergoing a 

 further division, they would give rise to potential female germ- 

 cells, seeing that the number 512 is that which Beard found 

 gave rise to female skates ; or to reverse the order, if instead of 

 512 germ-cells — potential females — the division had stopped 

 short at 256, then potential male germ-cells would have 

 resulted. In other words it might be assumed that sex was 

 determined by the division or otherwise of the 256 primary 

 germ-cells. This, however, is not so ; it is the egg prior to 

 fertilization which bears the characteristics of sex, and is either 

 male or female. It must therefore follow that the sex of the 

 embryo is determined at fertilization : not by the act as a 

 cause, but by the kind of egg — male or female — which has been 

 fertilized, male-eggs giving rise to male organisms and female- 

 eggs giving rise to female organisms. It must, of course, 

 follow that when once the egg is fertilized Hotliiiig whatever 

 can influence the sex of the offspring. 



It must further be noted that the primary germ-cells of 

 the skate, whether they belong to the 256 or the 512 series, 

 are exactly alike in size, each being 0*02 m.m. in diameter, 

 thus pointing to the probability of there being a difference in 

 the dimensions of the germinal disc from which they arise. 

 This is an established fact, for the segmented hemisphere 

 giving rise to the 512 primary germ-cells has a diameter of 

 1-2 m.m., and that giving rise to the 256 has but a diameter of 

 0-95 m.m. 



