196 THE FUNDAMENTAL ASPECT OF COLORATION 



for the more ardent selectionists to prove that it is forced upon 

 the organism by the stress of competition. 



(a) There is reason to beheve that carotinoid pigments, for 

 example, are widely spread among insects, and their absorption 

 occurs incidentally along with the food. Insects store up fat 

 in their adipose tissue, and carotin, being fat-soluble, becomes 

 deposited at the same time. Palmer and Knight's observations 

 have shown that, in the Reduviid bug Perillus, carotin under 

 ordinary conditions becomes stored in the integument in an 

 unoxidised state. If the temperature be raised sufficiently it 

 becomes entirely eliminated from the body, presumably after 

 oxidation. We can safely say that many caterpillars, whose 

 digestive secretions contain no enzymes which destroy carotinoid 

 pigments, will assume a yellow coloration if they feed upon 

 parts of plants in which carotin is the predominating colouring 

 material. 



Gerould, as has been previously mentioned, has described a 

 clear case of the inheritance of a factor which suppresses 

 carotinoid pigment in caterpillars of Colias philodice. The 

 recessive mutants in which this occurs are blue-green, whereas 

 the normal caterpillars are leaf-green, owing it would seem to an 

 admixture of carotinoid pigment. Gerould formulates the 

 conclusion that the nuclei of the intestinal epithelial cells, and 

 especially their chromosomes, produce an inheritable enzyme, or 

 recessive gene, capable of inhibiting or decolorising the carotinoid 

 pigments during the digestive processes. This mutant is therefore 

 essentially physico-chemical in nature and is apparently of negative 

 survival value. He mentions that an outdoor culture of larvae 

 comprising individuals of both colour types was exposed to the 

 attacks of sparrows for a period of twelve days. During that time 

 the conspicuous blue-green examples were almost all taken by 

 the birds, while many of the grass-green normally coloured larvai 

 were unmolested. 



(b) With regard to the coloration of Lepidopterous larvae by 

 means of derived chlorophyll, the most significant fact is the 

 absence of any enzyme or other chemical constituent destructive 

 to that pigment. We have no evidence whether chlorophyll 



