66 MENDELISM AND HEREDITY OF SEX 



single X chromosome. There still remains the 

 difficulty of explaining why the male gametocytes 

 after reduction develop into similar sperms, with 

 their heads and long flagella, although half of them 

 possess one X chromosome each and the other half 

 none. We can only suppose that the final develop- 

 ment of the sperms is the result of the presence of 

 the single X chromosome in the successive genera- 

 tions of male gametocytes before the reduction 

 divisions. 



The Mendelian theory of sex-heredity assumed that 

 in the reduction divisions the two sex-characters, 

 maleness and f emaleness, were segregated in the same 

 way as a pair of somatic allelomorphs, but the words 

 maleness and femaleness expressed no real concep- 

 tions. The view above suggested merely attempts 

 to bring our real knowledge of the difference be- 

 tween ovum and sperm into relation with our real 

 knowledge of the sex-chromosomes and their 

 behaviour in reduction and fertilisation. 



