154 SEXUAL SELECTION: BIRDS. [Pari II. 



in this manner when nearly mature, notwithstanding 

 that they were exposed to some additional danger, 

 might survive, and, from being favored through sexual 

 selection, would procreate their kind. The brightly-col- 

 ored young males being destroyed and the mature ones 

 being successful in their courtship may account, on the 

 principle of a relation existing between the period of 

 variation and the form of transmission, for the males 

 alone of many birds having acquired and transmitted 

 brilliant colors to their male offspring alone. But I by 

 no means wish to maintain that the influence of age 

 on the form of transmission is indirectly the sole cause 

 of the great difference in brilliancy between the sexes of 

 many birds. 



As with all birds in which the sexes differ in color, 

 it is an interesting question whether the males alone 

 have been modified through sexual selection, the fe- 

 males being left, as far as this agency is concerned, 

 unchanged or only partially changed ; or whether the 

 females have been specially modified through natural 

 selection for the sake of protection, I will discuss this 

 question at considerable length, even at greater length 

 than its intrinsic importance deserves ; for various cu- 

 rious collateral points may thus be conveniently consid- 

 ered. 



Before we enter on the subject of color, more espe- 

 cially in reference to Mr. Wallace's conclusions, it may be 

 useful to discuss under a similar point of view some other 

 differences between the sexes. A breed of fowls formerly 

 existed in Germany 6 in which the hens were furnished 

 with spurs ; they were good layers, but they so greatly 

 disturbed their nests with their spurs that they could not 

 be allowed to sit on their own eggs. Hence at one time 



6 Bechstein, ' "Naturgesch. Deutschlands,' 1*793, B. iii. s. 339 



