230 The Descent of Man. Pakt II. 



is transmitted, jet it probably is s'l, as all shades of colour are 

 strongly inherited by the horse. Nor is this foriu of inheritance, 

 as limited by the seasons, more remarkable than its limitation 

 by age or sex. 



Inheritaiire as Limited hy Sex. — The eqnal transmission oi 

 ciiaracters to both sexes is the commonest form of inheritance, 

 at least with those animals which do not present strongly-marked 

 sexual differences, and indeed with many of these. But characters 

 are somewhat commonly transferred exclusively to that sex, in 

 which they first appear. Ample evidence on this head has been 

 advanced in my work on ' Variation under Domestication,' but a 

 few instances may here be given. There are breeds of the sheep 

 and goat, in which the horns of the male differ ai-eatly in shape 

 from those of the female ; and these ditferences, acquired under 

 domestication, are regularly transmitted to the same sex. As a 

 rule, it is the females alone in cats which are tortoise-shell, 

 the corresponding colour in the males being rusty-red. With 

 most breeds of the fowl, the characters proper to each sex 

 are transmitted to the same sex alone. So general is this form 

 of transmission that it is an anomaly when variations in certain 

 breeds are transmitted equally to both sexes. There are also 

 certain sub-breeds of the fowl in which the males can hardly be 

 distinguished from one another, whilst the females differ con- 

 siderably in colour. The sexes of the pigeon in the parent-specits 

 do not differ in any external character ; nevertheless, in certain 

 domesticated breeds the male is coloured differently from the 

 female.'" The wattle in the English Carrier pigeon, and the crop 

 in the Pouter, are more highly developed in the male than in the 

 female ; and although these characters have been gained through 

 long-continued selection by man, the slight differences between 

 the sexes are wholly due to the form of inheritance which has 

 prevailed ; for they have arisen, not from, but rather in opposi- 

 tion to, the wish of the breeder. 



Most of our domestic races have been formed by the accumula- 

 tion of many slight variations; and as some of the successive 

 steps have been transmitted to one sex alone, and some to both 

 sexes, we find in the different breeds of the same species all 

 gradations between great sexual dissimilarity and complete 

 similarity. Instances have already been given with the breeds 

 jf the fowl and pigeon, and under nature analogous cases are 



" Dr. ChHpuis, ' Le Pigeon Voya- similar differences in certain breeds 



geur Beige,' 186.5, p. 87. Boitaru at Modena, ' Le variazioni del 



rt Corbie, ' Les Pigeons de Vo?iire,' Colombi domestici,' del Paolo Bo 



tc, 1824, p. 17.S. See, also, en niiii, 1873. 



