LIGHT AND PIGMENTATION 



83 



inconspicuous as possible and obliterate itself in its environment ; 

 and, as we shall see, this faculty of mimicey or homochromatism is 

 sometimes carried to almost unbelievable lengths, particularly among 

 teleostean fishes, the animal not only changing its general appearance 

 in light and shade but assuming the pattern of colour — blue, red, 

 yellow, green, black — of its surroundings (Fig. 53). 



Fig 



-The Eukopkan Plaice 





LEV ROy EVTES PLA 2'Et<SA . 



Lying in shallow water on the hed of the sea, to harmonize with wliieh 

 it is able to change its colovir within wide limits. The camouflage in tlie 

 figure is obvious (photograph by Douglas P. Wilson). 



Occasionally the opposite type of beliaviour is apparent and instead of 

 changing its coat to suit its environment, the animal alters its surroundings to 

 sviit its own coloration : tlius the sihery young of the Malayan sj^ider, Cyclosa 

 insulana, normally rests on a silvery silk platform, but as the animal becomes 

 older and brown in coloiu', it covers the platform with brown debris (Bristowe, 

 1941). In other cases a suitable environment is deliberately chosen ; thus the 

 desert lark. Aynmomanea, will settle with great reluctance on a terrain not of its 

 own colouring such as black lava, red earth, or light sand (Meinertzhagen, 1940), 

 just as bark-like moths will adopt postures that make their disrupted wing-design 

 conform with the configuration of the background (Cott. 1940). In still other 

 cases an artificial camouflage is assumed, such as the beetles or dressing-crabs 

 which drape themselves throughout life with a clothing of leaf -fragments, sticks 

 or weeds suitable to each successi^^e en\'ironment, or the geometrid lar\-a of 

 Borneo which similarly adorns itself with flower-buds (Shelford, 1902). 



DEMONSTRATIVE COLOTR CHANGES, although less conuuon, may 

 also be striking plienomena. These changes in colour whereby the 



