Januaet 8, 1909] 



SCIENCE 



63 



body, and, as shown by Miss Stevens and 

 others, they -undergo no reduction. All 

 these eggs produce females; but the male 

 tendency must be present in a latent or 

 recessive form, since males are ultimately 

 produced without fertilization. In the 

 maturation of the male-producing egg but 

 one polar body is formed and no general 

 reduction occurs. But, as already stated, 

 the males nevertheless contain one chromo- 

 some fewer than the females, and the male 

 egg must, therefore, in some way eliminate 

 one chromosome, i. e., reduction occurs in 

 the case of one chromosome-pair. It can 

 hardly be doubted that this pair is formed 

 by the two X-elements (accessory chromo- 

 somes). At first sight, therefore, the con- 

 clusion seems inevitable that one of the X- 

 elements bears the female tendency, the 

 other, the male. It is probable that a 

 similar process occurs in the bee and the 

 ant. In the latter cases the eggs must, of 

 course, originally bear the female tend- 

 ency; but after' the formation of both 

 polar bodies all bear the male tendency; 

 and it seems again at first sight impos- 

 sible to avoid the conclusion that the 

 female tendency is eliminated in the 

 course of maturation. The same conclu- 

 sion is indicated by Maupas's results on 

 Hydatina. 



It is evident from these facts that the 

 explanation of sex-production is to be 

 sought in a mechanism that is essentially 

 similar to that involved in alternative 

 heredity, and that a strong case can be 

 made out for the Mendelian interpretation 

 on this basis. This interpretation has 

 been worked out in three forms, which 

 exhaust the a priori possibilities. These 

 are, first, that both sexes are sex-hybrids or 

 heterozygotes (Castle) ; second, that the 

 male alone is a heterozygote, the female 

 being a homozygote recessive (Correns) ; 

 third, that the 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 fertiliza- 

 tion formulas would be 



Egg $ + spermatozoon ^^ = zygote 2(<S) ( female ) 



Egg c? + spermatozoon J = zygote c? ( 5 ) ( male ) 



or 



^Sg S + spermatozoon jj;=; zygote (2)^ (male) 



Egg d' + spermatozoon 2 = zygote {^)2 (female) 



according as the dominant character is 

 borne by the egg or the spermatozoon. In 

 either case a selective fertilization must be 

 assumed, since only gametes bearing op- 

 posite tendencies unite. 



This interpretation encounters two prin- 

 cipal difficulties. One is the necessity of 

 assuming selective fertilization, 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 aU the eggs after forming both 

 polar bodies produce males if unfertilized, 

 females if fertilized. Under the hypothe- 

 sis, therefore, the female tendency must be 

 derived from the spermatozoon. But this 

 is a reductio ad absurdum; for the male is 

 derived from an unfertilized egg which 

 has by the hypothesis eliminated the female 

 tendency. Castle offered the very ingen- 

 ious 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 

 (Agemiaspis, Litomastix) and that of 

 Schleip on the ant (Formica), which 

 clearly proves that the products of the 

 polar bodies in these forms do not in fact 

 enter into the composition of any part of 

 the body, yet the sexual relations are the 

 same as in the bee. This difficulty seems 

 to me to constitute a formidable obstacle 



