BIRDS-DEVELOPMENT OF SPURS. 443 



the cases of sexually-limited transmission can thus be accounted 

 for. It was further shown that if a male hird varied by becoming 

 brighter whilst young, such variations would be of no service 

 until the age for reproduction had arrived, and there was compe- 

 tition between rival males. But in the case of birds living on the 

 ground and commonly in need of the protection of dull colors, 

 bright tints would be far more dangerous to the young and in- 

 experienced, than to the adult males. Consequently the males 

 which varied in brightness whilst young would suffer much de- 

 struction and be eliminated through natural selection; on the 

 other hand, the males which varied in tliis manner when nearly 

 mature, notwithstanding that they were exposed to some addi- 

 tional danger, might survive, and from being favored through 

 sexual selection, would procreate their kind. As a relation often 

 exists between the period of variation and the form of transmis- 

 sion, if the bright-colored young males were destroyed and the 

 mature ones were successful in their courtship, the males alone 

 would acquire brilliant colors and would transmit them exclusive- 

 ly to their male offspring. But I by no means wish to maintain 

 that the influence of age on the form of transmission, is the sole 

 cause of the great difference in brilliancy between the sexes of 

 many birds. 



¥/hen the sexes of birds differ in color, it is interesting to 

 determine whether the males alone have been modified by sexual 

 selection, the females having been left unchanged, or only par- 

 tially and indirectly thus changed; or whether the females have 

 been specially modified through natural selection for the sake of 

 protection. I will therefore discuss this question at some length, 

 even more fully than its intrinsic importance deserves; for va- 

 rious curious collateral points may thus be conveniently con- 

 sidered. 



Before we enter on the subject of color, more especially in 

 reference to Mr. Wallace's conclusions, it may be useful to dis- 

 cuss some other sexual differences under a similar point of 

 view. A breed of fowls formerly existed in Germany" 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 

 it appeared to me probable that with the females of the wild 

 Gallinaceae the development of spurs had been checked through 

 natural selection, from the injury thus caused to their nests. 

 This seemed all the more probable, as wing-spurs, which would 

 not be injurious during incubation, are often as well-developed 

 in the female as in the male; though in not a few cases they are 



• Bechstein, 'Naturgesch. Deutschlands," 1793, B. iii. s. 339. 



