x COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX 299 



Concluding Remarks. 



The general principles of colour development now sketched 

 out enable us to give some rational explanation of the 

 wonderful amount of brilliant colour which occurs among 

 tropical animals. Looking on colour as a normal product of 

 organisation, which has either been allowed free play, or has 

 been checked and modified for the benefit of the species, we 

 can see at once that the luxuriant and perennial vegetation of 

 the tropics, by affording much more constant means of con- 

 cealment, has rendered brilliant colour less hurtful there than 

 in the temperate and colder regions. Again, this perennial 

 vegetation supplies abundance of both vegetable and insect 

 food throughout the year, and thus a greater abundance and 

 greater variety of the forms of life are rendered possible, than 

 where recurrent seasons of cold and scarcity reduce the 

 possibilities of life to a minimum. Geology furnishes us with 

 another reason, in the fact, that throughout the tertiary period 

 tropical conditions prevailed far into the temperate regions, so 

 that the possibilities of colour development were still greater 

 than they are at the present time. The tropics, therefore, 

 present to us the results of animal development in a much 

 larger area and under more favourable conditions than 

 prevail to-day. We see in them samples of the productions of 

 an earlier and a better world, from an animal point of view ; 

 and this probably gives a greater variety and a finer display of 

 colour than would have been produced, had conditions always 

 been what they are now. The temperate zones, on the other 

 hand, have recently suffered the effects of a glacial period of 

 extreme severity, with the result that almost the only gay 

 coloured birds they now possess are summer visitors from 

 tropical or sub -tropical lands. It is to the unbroken and 

 almost unchecked course of development from remote geo- 

 logical times that has prevailed in the tropics, favoured by 

 abundant food and perennial shelter, that we owe such superb 

 developments as the frills and crests and jewelled shields of 

 the humming-birds, the golden plumes of the birds of paradise, 

 and the resplendent train of the peacock. This last exhibits to 

 us the culmination of that marvel and mystery of animal colour 

 which is so well expressed by a poet -artist in the following 



