THE HEREDITY OF SEX 55 



zygote which is formed by the union of two sexes. 

 The quality of maleness consists only in the size, 

 form, and mobility of the sperm in the higher 

 animals and of the microgamete in other cases. 

 In what sense then can an ovum be male ? It 

 may perhaps be said that though it is itself female, 

 it has some property or factor which when united 

 with a sperm causes the zygote to be capable of 

 producing only sperms, and conversely the female 

 ovum has a quality which causes the zygote to 

 produce only ova. But since these qualities segre- 

 gate in the reduction divisions, how is it that the 

 male quality in the / ovum does not make it a 

 sperm ? We are asked to conceive a quality, or 

 the absence of a factor, in an ovum which is incapable 

 of causing that ovum to be a sperm, but which, when 

 segregated in the gametes descended from that ovum, 

 causes them all to be sperms. It is impossible to 

 conceive a single quality or factor which at differ- 

 ent times produces directly opposite effects. The 

 Mendelian theory is merely a theory in words, 

 which have an apparent relation to the facts, but 

 which when examined do not correspond to any 

 real conceptions. 



However, we have to consider a number of re- 

 markable facts concerning the relation of chromo- 

 somes to sex. In the ants, bees, and wasps the 

 unfertilised ovum always develops into a male, 

 the fertilised into a female. The chromosomes 

 of the ovum undergo reduction in the usual way, 

 and are only half the number of those present in 

 the nucleus before reduction. We may call this 

 reduced number N and the full number 2N. The 

 ova developing by parthenogenesis and giving 



