TROPICAL NATURE 



the large brilliantly -marked wings of some butterflies and 

 moths. 



Colours are produced or intensified by processes of develop- 

 ment, either where the integument or its appendages undergo 

 great extension or modification, or where there is a surplus of 

 vital energy, as in male animals generally, and more especially 

 at the breeding season. 



Colours are also more or less influenced by a variety of 

 causes, such as the nature of the food, the photographic or 

 physiological action of light, and also by some unknown local 

 action, probably dependent on chemical peculiarities in the soil 

 or vegetation. 



These various causes have acted and reacted in a variety 

 of ways, and have been modified by conditions dependent on 

 age or on sex, on competition with new forms, or on geo- 

 graphical or climatic changes. In so complex a subject, for 

 which experiment and systematic inquiry have done so little, 

 we cannot expect to explain every individual case, or solve 

 every difficulty ; but it is believed that all the great features of 

 animal coloration and many of the details become explicable 

 on the principles we have endeavoured to lay down. 



It will perhaps be considered presumptuous to put forth 

 this sketch of the subject of colour in animals as a substitute 

 for one of Mr. Darwin's most highly elaborated theories 

 that of voluntary or perceptive sexual selection ; yet I ven- 

 ture to think that it is more in accordance with the whole of 

 the facts, and with the theory of natural selection itself ; and 

 I would ask such of my readers as may be sufficiently in- 

 terested in the subject, to read again chapters xi. to xvi. of 

 the Descent of Man, and consider the whole subject from the 

 point of view here laid down. The explanation of almost all 

 the ornaments and colours of birds and insects as having been 

 produced by the perceptions and choice of the females, has, 

 I believe, staggered many evolutionists, but has been pro- 

 visionally accepted because it was the only theory that even 

 attempted to explain the facts. It may perhaps be a relief 

 to some of them, as it has been to myself, to find that the 

 phenomena can be conceived as dependent on the general 

 laws of development, and on the action of " natural selection," 

 which theory will, I venture to think, be relieved from an 



