198 HEREDITARY CHARACTERS 



female is the heterozygote, the male being a homozygote 

 recessive (Bateson). I will very briefly examine each of 

 these hypotheses. 



" The earliest of the three was that of Castle, according 

 to which the fertilisation formulae would be 



1 Egg 9 + spermatozoon $ = zygote $ ( $ ) (female) 

 Egg cJ + spermatozoon <? = zygote ( ? ) (male) 



or 



Egg 9 + spermatozoon $ = zygote ( ? ) ^ (male) 

 Egg $ -f- spermatozoon $ = zygote ( c? ) 9 (female) 



according as the dominant character is borne by the egg 

 or the spermatozoon. In either case a selective fertilisa- 

 tion must be assumed, since only gametes bearing opposite 

 tendencies unite. 



" This interpretation encounters two principal difficulties. 

 One is the necessity of assuming selective fertilisation, which, 

 though possible, seems a priori improbable. 



" The other is the case of the bee and some other 

 hymenoptera, which was pointed out by Castle himself, 

 but is now seen to be even more serious than he supposed. 

 In the bee, all the eggs after forming both polar bodies 

 produce males if unfertilised, females if fertilised. Under 

 the hypothesis, therefore, the female tendency must be 

 derived from the spermatozoon. But this is a reductio ad 

 absurdum; for the male is derived from an unfertilised 

 egg which has by the hypothesis eliminated the female 

 tendency. Castle offered the very ingenious explanation, 

 based on the results of Petrunkewitsch, that the testis is 

 derived from the polar bodies, which contain the female 

 tendency. But this exit from the difficulty seems to be 

 closed by the work of Sylvestri on certain of the Chalcidse 

 (Ageniaspis, Litomastix) and that of Schleip on the ant 

 (Formica), which clearly proves that the products of the 



' <J =male character, 9 = female. The signs in brackets are those which do 

 not appear in the individual containing them. 



