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. 
