212 TROPICAL NATURE, AND OTHER ESSAYS. 



birds — that, namely, in which the female is decidedly 

 brighter or more strongly marked than the male ; 

 as in the fighting quails (Turnix), painted snipe 

 {Ehynchcea), two species of phalarope (Phalaropus), 

 and the common cassowary {Casuarius galeatus). In 

 all these cases, it is known that the males take charge 

 of and incubate the eggs, while the females are almost 

 always larger and more pugnacious. 



In my ''Theory of Birds' Nests'' {Natural Selection, 

 p. 251), I imputed this difference of colour to the 

 greater need for protection by the male bird while 

 incubating ; to which Mr. Darwin has objected that the 

 difference is not sufficient, and is not always so distri- 

 buted as to be most effective for this purpose ; and he 

 believes that it is due to reversed sexual selection, that 

 is, to the female taking the usual role of the male, and 

 being chosen for her brighter tints. We have already 

 seen reason for rejecting this latter theory in every case ; 

 and I also admit that Mr. Darwin's criticism is sound, 

 and that my theory of protection is, in this case, only 

 partially, if at all, applicable. But the theory now 

 advanced, of intensity of colour being due to general 

 vital energy, is quite applicable ; and the fact that the 

 superiority of the female in this respect is quite excep- 

 tional, and is therefore probably not in any case of 

 very ancient date, will account for the difference of 

 colour thus produced being always very slight. 



Colow^'development as Illustrated by Humming-birds. 

 — Of the mode of action of the general principles of 

 colour- development among animals, we have an excellent 

 example in the humming-birds. Of all birds these are 

 at once the smallest, the most active, and the fullest of 



