v COLOURS OF ANIMALS 879 



is, by the supposition that colour and ornament are strictly 

 correlated with health, vigour, and general fitness to survive. 

 We have shown that there is reason to believe that this is 

 the case, and if so, conscious sexual selection becomes as 

 unnecessary as it would certainly be ineffective. 



Greater Brilliancy of some Female Birds 

 There is one other very curious case of sexual colouring 

 among 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 (Ehynchsea), 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" (see p. 132) 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 distributed 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 rdle 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 

 exceptional, 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. 



Colour-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 vital energy. 

 When poised in the air their wings are invisible owing to 

 the rapidity of their motion, and when startled they dart 



