BIRDS. 511 



dangerous to the young and inexperienced than to the 

 adult males. Consequently the males which varied in 

 brightness while young would suffer much destruction and 

 be eliminated through natural selection; on the other hand, 

 the males which varied 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. As a relation 

 often exists between the period of variation and the form 

 of transmission, 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 exclusively to their male off- 

 spring. 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. 



When 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 partially and indirectly thus changed; or whether 

 the females have been specially modified through natural 

 selection for the sake of protection. I will, therefore, dis- 

 cuss this question at length, even more fully than its intrin- 

 sic importance deserves ; for various curious collateral 

 points may thus be conveniently considered. 



Before we enter on the subject of color, more especially 

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

 useful to discuss some other sexual differences under a similar 

 point of view. A breed of fowls formerly existed in Ger- 

 many * 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 



*3echstein, " JJ^atur^esch. Deutscklands," 1793, B. iii, s. 339, 



