186 CAROTINOIDS AND RELATED PIGMENTS 



come colored by the lipochromes of the sponge upon which they live 

 as a parasite. Dastre (1899) noticed that he could suppress a 

 chlorophyll-like pigment which occurs normally in the liver of mol- 

 luscs by withholding chlorophyll-containing food, and that the pig- 

 ment was also absent from the liver at the end of the hibernation 

 period. Villard (1903) and Przibram (1906, 1907, 1909) found that 

 leaf lice which are raised on etiolated plants in the dark are mostly 

 pale yellow. Schneider (1908) mentions that he found that the crab- 

 eating perch, Perca fluviatilis, takes on the characteristic red color of 

 the crab in various places on its body. He thought that the pigment, 

 which he speaks of as crustaceorubin, took the place of a red pigment 

 which normally colors the fish, but it seems more likely that the 

 normal red pigment of the fish is the carotinoid derived from its food. 



A still more striking as well as very recent instance of biological 

 relationship affecting lipochromes is mentioned by Gerould (1921) in 

 connection with a blue-green mutation of the normally grass-green 

 caterpillar Colias (Euriinnix) Phiiadice, the blue mutant lacking 

 the normal lipochrome in its hemolymph, eye, cuticle, etc., and the 

 eggs of the butterfly from the blue mutant being pure white instead 

 of the usual yellow. The biological relationship involving the lipo- 

 chrome is between the caterpillar and the color of the cocoons spun 

 by the parasite Apanteles flaviconchce which emerges from it. These 

 cocoons are normally yellow from the normal, lipochrome containing 

 grass-green caterpillar, but were pure white from the blue-green 

 mutant which lacked lipochrome. According to Gerould, "Yellow 

 blood in silkworms is closely correlated with the spinning of yellow 

 silk, white blood with white silk. Ude (1919), however, has dis- 

 covered a strain of yellow stock that spins white silk, although their 

 silk glands are yellow." 



All of the above citations support the idea of a relationship between 

 plant and animal pigments and even between pigments among animals, 

 which is more than a mere chemical relationship or identity. An 

 especially striking argument supporting the existence of a general 

 biological relation such as is suggested by these instances is furnished 

 by the fact, pointed out by Beddard (1892), that there is a uniform 

 absence of pigment from cave animals coincident with the absence of 

 chlorophyll from cave plants. 



The number of scattered observations supporting this thesis is fairly 

 gratifying. Prior to the work of Palmer and Eckles (1914), however, 

 very few definite experiments were carried out which show the possi- 



