GilAP. VIII. SEXUAL SELECTION. 293 



our rule ; for it is generally caused by intemperance 

 after early youth, and is transmitted from the father 

 to his sons in a much more marked manner than to his 

 daughters. 



In the various domestic breeds of sheep, goats, and 

 cattle, the males differ from their respective females 

 in the shape or development of their horns, forehead, 

 mane, dewlap, tail, and hump on the shoulders; and 

 these peculiarities, in accordance with our rule, are not 

 fully developed until rather late in life. With dogs, 

 the sexes do not differ, except that in certain breeds, 

 especially in the Scotch deer-hound, the male is much 

 larger and heavier than the female ; and as we shall see 

 in a future chapter, the male goes on increasing in size 

 to an unusually late period of life, which will account, 

 according to our rule, for his increased size being trans- 

 mitted to his male offspring alone. On the other hand, 

 the tortoise-shell colour of the hair, which is confined 

 to female cats, is quite distinct at birth, and this case 

 violates our rule. There is a breed of pigeons in which 

 the males alone are streaked with black, and the streaks 

 can be detected even in the nestlings ; but they become 

 more conspicuous at each successive moult, so that this 

 case partly opposes and partly supports the rule. With 

 the English Carrier and Pouter pigeon the full develop- 

 ment of the wattle and the crop occurs rather late in 

 life, and these characters, conformably with our rule, 

 are transmitted in full perfection to the males alone. 

 The following cases perhaps come within the class pre- 

 viouslv alluded to, in which the two sexes have varied 

 in the same manner at a rather late period of life, and 

 have consequently transferred their new characters to 

 both sexes at a corresponding late period ; and if so, 

 such cases are not opposed to our rule. Thus there 

 are sub-breeds of the pigeon, described by Neumeis- 



