ACTION OF FORCES ON ORGANISMS. 51 



in the extreme north may be primarily due to the 

 small amount of light in those regions. i 



The arrangement of the pigments in organisms 

 seems to be governed by some peculiar law of 

 colour relations ; a law which seems to be deter- 

 mined more by the nature of light and of living 

 matter than by the particular nature of the organ- 

 ism. The existence of such a law is suggested by 

 the repetition of the same colours and combinations 

 of colours in widely different plants and animals. 

 Thus we find the brilliantly coloured spot on the 

 peacock's tail-feathers almost exactly reproduced 

 both in form and colour on the fins of certain fly- 

 ing-fish found among the Bahama Islands. Dr. 

 James McCosh has stated that patches of colours 

 which adjoin each other on plants and animals are 

 generally complementary colours, or else they are 

 separated only by a white or black streak. How 

 generally true this is may be observed in any good 

 collection of stuffed birds. But it is not univer- 

 sally true, as is shown by the brilliant Central 

 American macaw. This wonderful bird presents 



1 In all these cases the same colour prevails in all the classes of 

 animals, both in those which are offensive and those which are the 

 prey of others, and this universality of the colour seems not to be 

 wholly accounted for by the theory of protective colouration; never- 

 theless the view here advanced and the theory of protective coloura- 

 tion are in nowise mutually exclusive. 



