VI COLOURS OF CRUSTACEA AND ECHINODERMA 129 
Again, the red lipochrome is apparently capable 
of uniting with a complex organic base to form a 
blue compound, readily soluble in solutions containing 
albumen, which probably gives rise to the blue colours 
of many Crustacea. When mixed with the yellow 
pigment or with the red lipochrome, this blue 
pigment gives rise respectively to green and brown 
colours. 
It does not seem as yet possible to explain the 
absence of the blue and green colours from many 
Crustacea, and especially from those inhabiting deep 
water, but it may be noted that their continued 
persistence in the eggs is not very remarkable. Yolk 
is distinguished for the number of complex substances 
which it contains, especially such bases as neurin ; it 
may be that it is something of this nature which 
forms the lipochrome compound. 
From this description it is obvious that, in spite 
of the multiplicity of tints in the Crustacea, there is 
much uniformity of pigments—the lipochromes being 
fundamentally important in coloration. It is of some 
interest to note that the pigment called “ entero- 
chlorophyll” occurs at most only in very small amount 
and infrequently in connection with the digestive 
gland of Crustacea. Dr. M'Munn has described it 
there in some cases, but seems to have never obtained 
the complete spectrum ; in many cases it is certainly 
absent, and is probably never of great importance. 
The Colours of Echinoderma 
The colours of Echinoderms are almost as 
brilliant as those of the Crustacea, and are often of 
K 
