THE FACTORS WHICH DETERMINE SEX 679 



The view that sex is determined entirely by the ova had been 

 put forward some time previously by Beard, who stated that in the 

 skate, Raja batis, there were two kinds of eggs — one large, which 

 gave rise to females, and another small, which produced males. He 

 pointed out that there were two sizes of eggs in Hydatina senta, 

 Phylloxera, and Dinophilus apatris as well as in other animals, and 

 that these were related to sexual differences. 



It is also pointed out in support of Beard's view that according 

 to von Iheringi embryos which are found in one chorion (and which 

 are supposed, therefore, to have arisen from one ovum) in the 

 Edentate Praopus hybridus, are invariably of one sex, and that 

 " double monsters " in man are of the same sex, while Marchal ^ 

 states that in the chalcid fly {Ageniaspis fuscicollis), in which a 

 chain of embryos takes origin from a single egg, these eimbryos arp 

 all of one sex. 



The view has also been entertained that there is a relation 

 between the position of the ovary and the sex of the ova. Thus, 

 according to Eumley Dawson,^ the ova produced by the right ovary 

 become males, and those produced by the left become females. This 

 theory is believed to be applicable especially to man, and is based on 

 clinical evidence and on a supposed alternation of the sexes of the 

 eggs discharged at the ovulation periods. It clearly cannot apply 

 to birds, in which the left ovary only is functional, and King * has 

 shown experimentally that it is inapplicable to Amphibians. The 

 theory as well as the alternative one that sex depends on the 

 position of the testis from which the fertilising spermatozoon 

 was derived has been negatived by Copeman^ as a result of an 

 experimental investigation upon rats. 



Heape ® has expressed the belief that " each ovum and sperma- 

 tozoon in the generative glands contains within itself sex, which is 

 probably determined by the laws of heredity, but that the proportion 

 • of those male and female ova and spermatozoa which are developed 

 and ' set free from the generative glands may be regulated by 

 selective action, exerted in accordance with the resultant of a variety 



1 Von Ihering, " Ueber Generations-wechsel bei Saugethieren," Biol. 

 Centralhl., vol. vi., 1886. Newman, The Biology of Twins, Chicago, 1917. 



2 Marchal, " Eecherches «ur la Biologie et le Dgveloppenient des Hymenop- 

 tferes parasites," Arch, de la Zool. Exper. et Oen., vol. ii., 1904. 



^ Dawson, The Causation of Sex, London, 1909. 



* King, " Studies on Sex Determination in Amphibians," Biol. Bull., vol. xvi., 

 1909. 



5 Copeman, "Sex-Determination," Phys. Soc, May 1908 (unpublished). 

 The results were eventually published in abstract in Proa. Zool. Soc, 1919, 

 which contains further suggestive information. See also Doncaster and 

 Marshall, Jour, of Genetics, vol. i., 1910 ; and King, Jour, of Exp. Zool., vol. x., 

 1911. 



^ Heape, " Note on the Proportion of the Sexes in Dogs," Proc. Camb. Phil. 

 Soc, vol. xiv., 1907. 



