^6 Edmund B. Wilson 



of the sexes in accordance with the Mendehan principle without 

 the necessity for assuming selective fertilization. It is so simple, 

 and seems to be so clearly demonstrated in the case of Bryonia, 

 that its application to the interpretation of sex production in 

 general is very tempting. Correns himself believes it "very prob- 

 able" that his conclusion will apply to all the dioecious flowering 

 plants, and possible that it may also hold true of animals (op. cit., 

 pp. 65, 66). It is evident that in their superficial aspects the cyto- 

 logical results seem to bear this out. Wherever the sexes show 

 visible differences in the somatic chromosome groups the female 

 groups consist of two series in duplicate, while the male groups 

 show two series that are not duplicates, only one of them being 

 identical with one of the female series. As far as the chromosomes 

 are concerned, and from a purely morphological point of view, 

 the female is therefore in fact a homozygote, the male a hetero- 

 zygote, in these animals. But when more closely scrutinized 

 from this standpoint the interpretation seems by no means so 

 clear. As I showed in my third "Study" the odd chromosome 

 of the male must be derived from the egg; and if this chromosome 

 bears the sexual tendency, it must under Correns's hypothesis 

 carry the female tendency — ^which is a reductio ad absurdiim, 

 since it is not accompanied by a male-bearing mate or partner in 

 the male. I think this brings clearly into view the following alter- 

 native. Either the females of these insects must be physiolog- 

 ically heterozygotes (as I assumed), or the so-called "sex chromo- 

 somes" (idiochromosomes) do not bear the sexual tendencies but 

 only accompany them in a definite way. Which of these possi- 

 bilities is the true one may be left to further research to decide. 

 I will only point out that Professor Correns carefully considers the 

 difficulties that his interpretation encounters in some other direc- 

 tions, and admits that it must be modified in certain cases — for 

 example in the honey bee and in Dinophilus, in which latter case 

 he too is compelled to admit the possibility of selective fertiliza- 

 tion. The parthenogenetic females of such forms as the aphids 

 and phylloxerans, which produce both males and females without 

 fertilization, are still considered by Correns as homozygotes, the 

 production of males being assumed to be determined, if I under- 



