PIGMENTARY COLOURS 185 



were able to demonstrate that in the larva of the latter insect 

 the blood is coloured deep orange by carotin derived from the 

 potato plant. In the fresh blood of the beetle this pigment 

 occurs in a concentration amounting to 0-0136 per cent., which is 

 as high as that found in fresh green leaves. It is remarkable that 

 no xanthophyll could be detected in the blood, since there can be 

 scarcely any doubt that the green leaves of the potato plant are 

 as well endowed with this pigment as other plants. It appears, 

 therefore, that the Perillus, in the process of imbibing the blood 

 of its prey, obtains the carotin which so largely contributes to its 

 characteristic coloration. In both this bug and in its prey the 

 yellow and red colours of the integument are due to differences in 

 the degree of concentration of the same pigment. Knight (1924) 

 has shown that temperature, by influencing the physiological 

 processes during the active life of Perillus, indirectly affects the 

 coloration of that insect. When reared at a temperature of 

 85° to 95° F. white forms are produced, while at temperatures 

 below 78° F. the red and yellow forms appear. When subject to 

 the higher temperatures carotin is not deposited in the hypo- 

 dermis, and the insects void chalky white excreta. Under these 

 circumstances it appears that the carotin becomes oxidised, a 

 fact which Palmer and others had previously noted to take place 

 in animals having a high rate of metabolism. If white examples 

 of Perillus be subjected to a relatively cool environment (70° to 

 75° F.) they discharge normal excreta — dark reddish, brown or 

 black in colour, and at the same time commence to accumulate 

 carotin in the hypodermal cells. Humidity, it appears, does not 

 behave as an individual factor in the process, since it does not 

 exercise notable effect upon the coloration of the insect. A 

 relative humidity of 100 per cent, probably inhibits metabolism 

 in various ways, particularly by slowjng down physical activity, 

 and in this way a greater deposition of carotin might be expected. 



Evidence that xanthophyll plays a considerable part in insect 

 coloration is by no means established, and experiments by feeding 

 caterpillars on yellow maize, or other plants known to be rich in 

 this pigment, are greatly to be desired. 



In 1921 Gerould described a larval colour mutation in the Pierid 



