MENDELISM AND SEX 139 



former zygote will be a male, for the observations of 

 the three investigators just mentioned have shown 

 that the somatic or body cells of the males investigated 

 by them contain one chromosome less than the 

 body cells of the females. The latter zygote will 

 be a female, since it contains the full complement 

 of chromosomes. 



If these observations prove to be of general 

 application, then it would appear that sex is 

 determined by the presence or absence of the paired 

 condition of the accessory chromosome. If it is 

 paired in the zygote, femaleness results ; if it is 

 unpaired, then maleness results. But, whether the 

 zygote shall contain the paired or unpaired accessory 

 chromosome depends upon the kind of spermatozoon 

 by which fertilisation is effected. The male is 

 the arbiter which decides the result. 



These interesting discoveries in connexion with 

 the chromosomes of cells enable us to frame explana- 

 tions of several things which were previously in- 

 capable of any satisfactory or consistent statement. 

 We may therefore next turn our attention to the 

 new interpretation of old facts which these dis- 

 coveries enable us to frame. 



As is well known, the eggs laid by the queen 

 bee are some of them fertilised and some not. But 

 both sorts of eggs develop. The unfertilised ones, 

 however, give rise to the male drones, while the 

 fertilised eggs produce the w^orkers, which are im- 

 mature or imperfect females. In order to understand 



