^g^ Comparative Animal Physiology 



Adapti\e morphological color changes in response to background have also 

 been reported For the chromatophores of crustaceans^''- " and for melano- 

 phorcs,'''' lipophores,' and guanophores^'*'' of a number of fishes. Functional 

 melanophores have been induced to form on the normally unpigmented ven- 

 tral surface of flounders either by placing normal fish in black tanks illum- 

 inated from below, or by blinding the animals and illuminating them from 



below.'-- 



The influence of a black background may be simulated in many animals 

 by opaquing the lower half of the eye. This has been demonstrated for the 

 walking-stick, Dixippiis,^^- '-^^ the shrimps, Palaemonetes^'-' and Leander,^'^ 

 and teleost fishes."*" 



The character of the influence of light in the secondary color responses of 

 animals is obviously one especially adapted to provide the animal with a 

 certain degree of protective or obliterative coloration with respect to its back- 

 ground. As might be anticipated, the function appears in general better de- 

 veloped in animals which are bottom dwellers, or which spend much of 

 their time quietly attached to objects, than in forms which are more freely 

 mobile. 



The adaptation to color of background is in many instances by no means 

 restricted to simple blanching and darkening on white and black back- 

 grounds, respectively. Adaptations of the prawn, Hippolyte, to many colors 

 and tints of background were described many years ago."*^' ^^"^ More recently 

 it has been shown that Crago will change its coloration to match red and 

 vellow backgrounds, in addition to black and white."^ Palaemonetes has been 

 shown to change its color within a few days to accord with black, white 

 red, yellow, blue, or green backgrounds.--^ The crab, Portiinus ordivayi, adapts 

 to black, white, red, and yellow,- as does also Planes.*''* The eephalopod, Se- 

 pia, becomes gr?en on a green background and yellow on a yellow one.'**- 



Some of the most striking examples of color adaptation in \'ertebrates are 

 seen in flatfishes. The changes in the flounder Paralichthys alhignttus on red, 

 green, yellow, and blue backgrounds have been described.^"^- *'" This fish, 

 moreover, is able to simulate rather strikingly the color pattern of the back- 

 ground, thus rendering its protective coloration even more effective. Many 

 other teleosts and amphibians are able to show yellow tints in response to 

 yellowish backgrounds. 



These adaptations to color of background are the results of appropriate 

 differential movements of the various pigments within the chromatophores, 

 supplemented by morphological color changes to reinforce these physiological 

 ones. In these activities the animal may show the capacity for inducing 

 changes in the distributions or amounts of its various pigment types more 

 or less independently of one another, thus indicating complex mechanisms 

 of chromatophore control. Species may be limited in the colors of back- 

 ground to which they can adapt themselves, through lack of suitably col- 

 ored pigments. For example, Crago lacks blue pigment and hence is unable 

 to adapt to either blue or green. Palaevionetes, possessing red, yellow, and 

 blue pigments, can, bv a[>propriate pigment manipulation, become almost 

 any color, including black. On the other hand, some species possess pigments 

 of particular colors yet appear to show no ability to adapt to backgrounds 



