580 Comparative Animal Physiology 



In insects the epidermal cells themselves serve as functional chromato- 

 phores. During darkening of the skin the dark brown-black pigment within 

 these cells migrates from small concentrated masses below an evenly dis- 

 persed yellow and green pigmented layer to a more superficial position, 

 where it disperses (Fig. 256). The red pigment in skin darkening disperses 

 from small spherical masses to form a continuous sheet of pigment.*"^ Thus 

 the forces which operate in pigment concentration and dispersal in chroma- 

 tophores in general are apparently of such a nature as can operate within 

 the limits of more conventionally shaped cells. Migration of a red hemato- 

 chrome pigment in Euglena, from a deeper position in the body internal to 

 the chloroplasts to a dispersed, superficial position, results in a green to red 

 color change in response to elevated light intensity.*^'*- ^^ 



2 



Fig. 256. Diagrammatic sections thru the epidermis of Hght (upper) and dark (lower) 

 adapted Dixippus. The coarsest stippling (3) indicates brown-black pigment; the inter- 

 mediate stippling (2), red pigment; and the finest (1), yellow-green pigment. From 

 Giersberg."* 



In and associated with the chromatophores of crustaceans are a number 

 of different colors of pigments. The kinds which are present vary with the 

 species and even occasionally among individuals within the same species 

 having different histories. Yellow and red fat-soluble pigments appear to be 

 of quite general occurrence within the group. These are carotene deriva- 

 tives.'**' ^°^ Also of quite general presence is a reflecting white pigment which 

 has been described as guanin. The majority of the macruran decapods pos- 

 sess a transparent blue pigment, which is a carotenoid conjugated with a 

 protein (carotenalbumin).^'"' In fact the application of heat or alcohol to in- 

 tegument containing the blue pigment results in its rapid transformation from- 

 a water-soluble blue to a fat-soluble red pigment. Finally, in certain crusta- 

 ceans a black or brownish-black pigment is present. This pigment, a melanin, 

 is found in Crago among the macrurans, in many true crabs, and in manv 

 isopods. 



