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 



