VIII ORIGIN AND USES OF COLOUR IN ANIMALS 227 



bring it clown within easy reach of the net, especially if it be 

 of the opposite sex."^ In a great number of insects, no doubt, 

 form, motions, stridulating sounds, or peculiar odours, serve to 

 distinguish allied species from each other, and this must be 

 especially the case with nocturnal insects, or with those whose 

 colours are nearly uniform and are determined by the need of 

 protection ; but by far the larger number of day-flying and 

 active insects exhibit varieties of colour and marking, forming 

 the most obvious distinction between allied species, and which 

 have, therefore, in all probability been acquired in the process 

 of differentiation for the purpose of checking the intercrossing 

 of closely allied forms."- 



Whether this jirinciple extends to any of the less highly 

 organised animals is doubtful, though it may perhaps have 

 affected the higher mollusca. But in marine animals it seems 

 prol^able that the colours, however beautiful, varied, and 

 brilliant they may often be, are in most cases protective, 

 assimilating them to the various bright-coloured seaweeds, or 

 to some other animals which it is advantageous foi- them to 

 imitate.^ 



Summary of the Preceding Exposition. 



Before proceeding to discuss some of the more recondite 

 phenomena of animal coloration, it will be well to consider 

 for a moment the extent of the ground we have already 

 covered. Protective coloration, in some of its varied forms, 

 has not improbably modified the appearance of one-half of 

 the animals living on the globe. The white of arctic animals, 

 the yellowish tints of the desert forms, the dusky hues of 

 crepuscular and nocturnal species, the transparent or bluish 

 tints of oceanic creatures, represent a vast host in themselves; 

 but we have an equally numerous liody whose tints are 

 adapted to tropical foliage, to the bark of trees, or to the soil 



^ Quoted by Darwin in Descent of Man, p. 317. 



- lu the American Naturalist of Marcli 1888, Mr. J. E. Todil has an 

 article on " Directive Coloration in Animals," in which he recognises many of 

 the cases here referred to, and suggests a few others, though I tliink he 

 includes many forms of coloration — as " paleness of belly and inner side of 

 legs " — which do not belong to this class. 



* For numerous examples of this protective colouring of marine animals 

 see Moseley's Vo)jaf/e of the Challenrjer, and Dr. E. S. Morse in Proc. of Bost. 

 Soc. of Nat. Hist., vol." xiv. 1871. 



