172 CAROTINOIDS AND RELATED PIGMENTS 



red carotinoid by heat, acids, alcohol, ether, etc. The author sug- 

 gests a colloidal explanation for the hitherto inexplicable relations 

 between these apparently water-soluble chromogens and the red 

 pigment. 



The same red and yellow "carotinoicl-like pigments found in Crus- 

 tacea appear to be the cause of like colorations among the echino- 

 derms (starfish, brittle-stars, sea-urchins, etc.). In addition, red, 

 green, blue and violet lipochromogens are also encountered. 



The shells of snails apparently may be colored by the red caroti- 

 noid-like pigment already described, and the digestive organs of these 

 animals as well as some molluscs may contain a pigment which is 

 either carotin or xanthophyll or a modification of one of these 

 carotinoids. 



The brilliant colors encountered among marine and fresh water 

 worms are due in part to carotin or related pigments. Similar colors 

 among the sea-anemones, corals, jelly-fish and related animals, how- 

 ever, do not appear to involve the carotinoids. 



The yellow, orange and red colors of sponges have been found to 

 be due almost exclusively to lipochromes in the broad sense. The 

 yellow and orange pigments are undoubtedly true carotinoids, and 

 the red pigment is the carotin-like substance, showing one absorp- 

 tion band, which is so widely distributed among lower forms of ani- 

 mal life. The presence of both carotin and xanthophylls is indicated 

 among the true carotinoids. 



