636 THE PHYSIOLOGY OF REPRODUCTION 



be determined prior to the final phenomena of the reduction 

 and of the ripening, for these latter would not appear to possess 

 any influence on the size of the egg itself." l Beard states that 

 the eggs of the skate, Raja batis, are likewise of two kinds. It 

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

 to von Ihering 2 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 3 states that in the chalcid fly (Ageniaspis fuscicollis) 

 in which a chain of embryos takes origin from a single egg, 

 these embryos are all of one sex. (See footnote 2 , p. 657.) 



Beard asserts that sex is determined solely in the egg, and 

 that in those animals in which there are two kinds of spermatozoa 

 one land is always functionless. This theory is clearly opposed 

 by the facts discovered by Wilson regarding the spermatozoa of 

 many insects, and by the case of the bee and other forms in which 

 sex is determined by fertilisation. It must be pointed out, 

 however, that, according to Morgan, in the parthenogenetic 

 Phylloxera, the egg has the power of determining sex by regu- 

 lating the number of its chromosomes in the same kind of 

 way as has been shown in the case of other insects for the 

 spermatozoon. 4 



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 Rumley Dawson, 6 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 alterna- 

 tion 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 6 has shown experimentally that it is 



1 Beard, loc. cit. 



* Von Ihering, " Ueber Generations-wechsel bei Siiugethieren," Biol. 

 Centralbl., vol. vi., 1886. 



3 Marchal, " Recherches sur la Biologie et le Developpement des 

 Hymenopteres parasites," Arch, de la Zool. Exper. et Gen., vol. ii., 1904. 



* Morgan, Proc. Soc. Exp. Biol. and Med., loc. cit. 

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



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

 vol. xvi., 1909. 



