CAROTINOIDS IN INVERTEBRATES 171 



Summary 



Carotinoids arc abundantly present in the invertebrates lut they 

 cannot be said to predominate even among the pigments of yellow 

 to red eolor. As one descends the scale of animal forms non-carotinoid 

 pigments of yellow to red hues are encountered more and more fre- 

 quently. The simpler digestive apparatus of the lower animals does 

 not seem to insure a more abundant distribution of biologically de- 

 rived pigments. 



The orders of insects in which carotinoids occur are butterflies, bugs, 

 beotlrs and locusts (grasshoppers). In the butterflies it is the larvae 

 and pupae which contain carotinoids, not the butterflies themselves. 

 Although the chromolipoid, present chiefly in the haemolymph (blood) 

 of the larvae and pupae, and also in the eggs, has been known as 

 "xanthophyll" since the work of Poulton (1885) there is evidence to 

 suggest that the pigment is actually carotin. 



Among the bugs, the yellow pigment which can be extracted from 

 green plant lice (Aphids) is carotinoid in nature but it is not known 

 whether a single pigment or a mixture is concerned. Carotin itself 

 appears to be the cause of the red color of the tegument in the case 

 of certain other species of bugs. 



There can be no doubt that the yellow and orange pigments found 

 in the beetles are often, if not always, carotinoids. The red pig- 

 ment, however, belongs to the carotin-like pigments which conform 

 to the properties of the so-called carotinins described in previous 

 chapters. 



The character of the carotinoids which occur in many locusts and 

 grasshoppers is not known; the subject deserves further study. 



Two distinct types of chromolipoids are present in Crustacea, one 

 characterized by its red color, the other by a more yellow hue. All 

 the older investigations of the red pigment agree in showing that it 

 differs in its general properties from the known carotinoids only in 

 exhibiting one spectroscopic absorption band and in forming salts 

 with alkalies and alkaline earths. However, Verne (1920a, b) has 

 recently announced that the pigment is identical in every respect 

 with carotin. All the properties of the yellow pigments so far ex- 

 amined suggest carotin, rather than xanthophyll. 



The red crustacean carotinoid appears to exist in the shell of vari- 

 ous species as a water-soluble substance of blue, brown, orange or 

 green color, which is instantly transformed into the water-insoluble 



