VI COLOURS OF CRUSTACEA AND ECHINODERMA 133 
5. Holothuria .—Of the external colouring of the 
sea-cucumbers there is not much to say ; as a rule 
they tend to be dull and dark in tint. Black or 
brown colours are not uncommon, while greenish- 
violet or gray also occur. The relative dulness of 
the tints is curious in view of the fact that the 
pigments are numerous and often brilliant. 
The Pigments of Echinoderma 
1. The pigments of the star-fishes, as their colour 
and their distribution indicate, are largely lipochromes, 
and are probably very similar in nature to those 
of the Crustacea. As in the Crustacea, the pig¬ 
ments are not confined to the skin but occur also 
in the internal organs and especially in the ovary. 
M'Munn (1883) describes haematoporphyrin, on 
spectroscopic grounds only, in the integument of 
Asterias glacialis. He has also shown that entero- 
chlorophyll occurs in considerable amount in the 
digestive caeca. As to the nature of the blue and 
violet pigments of star-fishes, there is much more 
difficulty. Krukenberg describes a blue pigment in 
Astropecten miranticus which is soluble in water, and 
is readily turned red by the action of heat, alcohol, 
and other reagents. The blue pigment does not 
apparently affect the colour of the organism during 
life, and the blue colour is only apparent when the 
superficial lipochrome has been removed by alcohol. 
Krukenberg regarded this blue pigment as being in 
all probability identical with cyanein, the blue pig¬ 
ment of jelly-fish. It does not seem to be the same 
as the blue pigments of Crustaceans. 
