2G0 THE DESCENT OF MAN. 



animals in a state of nature, inniimenible instances occur 

 of characters appearing periodically at different seasons. 

 We see this in the horns of the stag, and in the fur of the 

 Arctic animals, which becomes thick and white during the 

 winter. Many birds acquire bright colors and other deco- 

 rations during the breeding-season alone. Pallas states,* 

 that in Siberia domestic cattle and horses become lighter- 

 colored during the winter; and I have myself observed, and 

 heard of similar strongly-marked changes of color, that is, 

 from brownish-cream color or reddish-brown to a perfect 

 white, in several ponies in England. Al though I do not know 

 that this tendency to change the color of the coat during 

 diiferent seasons is transmitted, yet it probably is so, as all 

 shades of color are strongly inherited by the horse. Nor is 

 this form of inheritance as limited by the seasons, more 

 remarkable than its limitation by age or sex. 



Inheritance as TAmited by Sex. The equal transmission 

 of characters to both sexes is the commonest form of inher- 

 itance, at least with those animals which do not present 

 strongly-marked sexual differences, and indeed with many 

 of these. But characters are somewhat commonly trans- 

 ferred 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 greatly in shape from 

 those of the female; and these differences 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 color 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 varia- 

 tions 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, while the females differ considerably in color. 

 The sexes of the pigeon in the parent-species do not differ 



* " Novae species Quadrupedum e Glirium ordine," 1778, p. 7. On 

 the transmission of color by the horse, see " Variation of Animals, 

 etc., under Domestication." vol. i, p. 51. Also vol. ii, p. 71, for a 

 general discussion on " Inheritance as Limited by Sex." 



