XL] MY NEW IDEAS 385 



coloured and tJie nest is open to view, tlie female is plainly 

 coloured and inconspicuous. No less than fifteen whole families 

 of birds and a number of the genera of other families belong 

 to the first class, of brightly coloured birds with sexes alike, 

 and they all build in holes or make domed nests. Most of 

 these are tropical, but the woodpeckers and kingfishers are 

 European. In the second class, however brilliant the male 

 may be, if the nest is open to view, the female is always 

 plainly coloured, sometimes so much so as to be hardly 

 recognizable as the same species. This is especially the case 

 in such birds as the brilliant South American chatterers and 

 the Eastern pheasants and paradise birds. This law is of 

 especial value, as showing the exceptional need of protection 

 of female birds as well as butterflies, and the remarkable way 

 in which the colours of both classes of animals have become 

 modified in accordance with this necessity. This paper forms 

 chapter vi. of my " Natural Selection and Tropical Nature." 



5. In the great subject of the origin, use, and purport of 

 the colours of animals, there are several branches which, I 

 believe, I was the first to call special attention to. The most 

 important of these was the establishment of the class of what 

 I termed " Recognition colours," which are of importance in 

 affording means for the young to find their parents, the sexes 

 each other, and strayed individuals of returning to the group 

 or flock to which they belong. But perhaps even more 

 important is the use of these special markings or colours 

 during the process of the development of new species adapted 

 to slightly different conditions, by checking intercrossing 

 between them while in process of development. It thus 

 affords an explanation of the almost universal rule, that closely 

 allied species differ in colour or marking even when the 

 external structural differences are exceedingly slight or quite 

 undiscoverable. The same principle also explains the general 

 symmetry in the markings of animals in a state of nature, 

 while under domestication it often disappears : difference of 

 colour or marking on the two sides would render recognition 

 difficult. This principle was first stated in my article on 



vol. 11. 2 C 



