COLORATION IN MAMMALS AND BIRDS. 187 



higli vigour exist, the majority of the animals will be brightly 

 coloured ; and suggestions are made to account for the apparent 

 exceptions to the rule, which suggestions, it is claimed, are borne 

 out by the distribution of the dark polar and light tropical 

 species. 



I further claim to have shown that, shortly before the moult 

 in many animals, the colour of the pelage fades, beginning along 

 certain definite areas and from certain centres which I call 

 '•'■ ■pcecilomeres^'' and that this bleaching is due to physiological 

 causes. 



Further, that ^'- poecilomeres '' maybe found throughout the 

 mammalian and avian series, as patches differing either in their 

 intensity or lack of colour from the surrounding portions, in 

 many cases conspicuous and cited as examples of warning, pro- 

 tection, &c. ; or, again, as marks so slight as to be unnoticeable 

 unless carefully looked for; or, again, merely appearing as 

 transitory patches during the growth of a new pelage or 

 plumage. 



Hence it is argued that these patches so universal, and in 

 many cases so inconspicuous, must owe their inception to internal 

 rather than external causes, and that we have here the basis of 

 diversity of colour, i. e. coloration. 



If these facts be accepted, both colour and coloration must be 

 due to physiological causes. 



The question of whether seasonal changes are produced by 

 moult or by colour change has purposely been entirely omitted 

 as belonging to a side issue. 



Natural selection and protective coloration have also been 

 left out, not because I do not believe in the great part they play, 

 but because, if my suggestion be near the truth, they are only 

 able to make use of those colours or modify those markings 

 which in the first place are supplied by vigour. 



