278 RECENT CYTOLOGY 



woman has normal children, while a colour-blind woman 

 married to a normal man has normal daughters and 

 colour-blind sons. Colour-blind men are frequent, 

 because the daughters of colour-blind men, though 

 normal themselves, transmit the affection to half their 

 sons; but colour-blind women are very rare, because 

 they can only be produced by the marriage of a colour- 

 blind man to a woman who is herself heterozygous for 

 the affection. 



In Moths and Butterflies, and also in Birds, exactly 

 the converse condition is found. In them, instead of 

 the male transmitting characters only to his daughters, 

 it is the female which transmits certain characters 

 only to her male offspring, while the male transmits to 

 sons and daughters alike. In Fowls, for example, if a 

 barred hen is mated with an unbarred cock, all the 

 cockerels will be barred and the pullets plain, while a 

 cock of a barred breed mated with an unbarred hen 

 produces barred chickens of both sexes. And in the 

 Currant Moth (Abraxas grossulariata] , in which this 

 form of sex-limited inheritance was first investigated, 

 it has been shown by Doncaster that, at least in certain 

 strains, the female has a single idiochromosome and 

 the male two i.e., exactly the converse condition of 

 that found in Protenor, etc. In this case, therefore, 

 there are two sorts of eggs, male -producing and female- 

 producing, but only one kind of spermatozoa, and it is 

 the male-producing eggs (those which have the extra 

 chromosome) which bear the sex-limited character. 



These facts, therefore, seem to prove that sex is 



