MENDELIAN EXPERIMENTS UPON SEX 200 



combination upon fertilisation would make it very improb- 

 able, but not impossible, that the entities controlling the 

 appearance of the sexes would be equal in any individual. 

 Such an event would happen but seldom. Hermaphrodites 

 do occur among organisms where the sexes are as a rule 

 separate, but they are rare. In the highest animal, man, 

 they are extraordinarily rare. This theory also accounts for 

 those cases where men show female characters and women 

 male characters. 



If this view of sex is correct, the secondary sexual char- 

 acters must be regarded as racial characters, but dependent 

 for their appearance upon the presence of one or other kind 

 of sexual cells, in fact, upon the primary sexual character. 

 We know that a particular reaction to given stimulus may 

 be a true racial character, so there is no reason against 

 supposing that the appearance of the secondary sexual 

 characters depends upon the presence or absence of some 

 stimulus such as an internal secretion of the sexual cells. 

 Indeed, that this is the case is suggested very strongly by 

 the experimental evidence already referred to. 1 



It seems very probable that the Mendelian interpretation 

 of some breeding experiments is due to the fact that the 

 alternative appearance 2 of the secondary sexual characters 

 has been overlooked. In an experimental cross between the 

 moth Abraxas grossulariata and its variety lacticolor, 3 it 

 was claimed that " sex determinants behave as Mendelian 

 characters," femaleness being dominant. The case may be 

 briefly stated as follows. When a female variant, lacticolor, 

 was crossed with a male grossulariata, males and females 

 were produced in roughly equal numbers. This continued 

 in subsequent generations, but no males with the lacticolor 

 characters were produced. From this it was concluded that 

 all the females were impure dominants (heterozygous) with 



1 See p. 205. 



2 Though potentially present the secondary sexual characters under ordinary 

 conditions only appear in the presence of the necessary stimulus, i.e. one or other 

 forms of germ cells. 



3 Doncaster, British Association Meeting, 1908. 



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