128 COLOUR IN NATURE chap. 



produced by a mixture of the blue compound and 

 unaltered red lipochrome. 



General Characters of Pigments 



Looking at the pigments of Crustacea in general, 

 it is seen that the red lipochromes form the central 

 pigments of the group. There occurs in addition 

 a widely spread yellow pigment, which does not 

 apparently give the lipochrome reaction, and whose 

 relation to the red remains doubtful. It is also 

 uncertain whether some of those changes from red 

 to yellow which have been described, are or are not 

 due to an actual change of the red pigment into the 

 yellow. On the other hand, there appears no doubt 

 that the red pigment in itself or in its modifications 

 is instrumental in the production of most of the 

 colours of the Crustacea. When the shell contains 

 little lime or is very thin, the red pigment present 

 in the shell and in the underlying skin gives rise to 

 bright red or scarlet tints. When the shell contains 

 much lime it is often of an orange tint, and is then 

 possibly coloured by a combination of the red 

 lipochrome with lime. It is at least certain that 

 the lipochrome does form orange-coloured combina- 

 tions with lime, soda, etc., and the colour and 

 insolubility of the pigment in the orange- coloured 

 shell of, e.g., Nephrops, suggest the presence of such 

 a combination there. This suggestion seems also 

 to explain the brightness of the tint in deep-sea 

 Crustacea where lime salts are virtually absent, 

 and in recently moulted specimens of the edible 

 crab before the development of the lime. 



