ii8 COLOUR IN NATURE chap. 



characters of the Crustacea, but it may be well to 

 mention some points which are of importance in 

 reference to the coloration. In the first place, we 

 may note that the Crustacea, like all other Arthro- 

 pods, have a firm cuticle of chitin. This chitinous 

 coat is not infrequently impregnated with lime salts, 

 and is in most cases pigmented. The subjacent 

 epidermis almost always contains pigment, either in 

 special contractile chromatophores, or in solution in 

 the general cells, or more usually in both. In some 

 cases, as in the adult lobster, the epidermis is so 

 completely concealed during life beneath the thick 

 cuticle that it is of practically no importance as 

 regards coloration, while in other cases the cuticle 

 is thin and translucent, and it is the epidermis which 

 is important in the production of surface coloration. 

 The degree of calcification is the most important 

 factor in the production of opacity in the cuticle, so 

 that in general terms we may say that the shell 

 or cuticle tends to be transparent in small forms, in 

 those inhabiting fresh water, and in abyssal forms. 



Colour-variation in Crustacea 



As a class the Crustacea are remarkable for the 

 brilliancy of their colours, blue, green, shades of 

 orange, pink, red, and brown being all common 

 tints. Nor are the bright colours confined to the 

 higher forms ; the tiny Daphnia forms vivid scarlet 

 patches on the surface of the sea, Diaptormis bacillifer 

 forms red patches in fresh- water lakes, and so on. 

 As a general rule, however, the colours harmonise 

 with the surroundings, this being especially true of 



