IV THE COLOURS AND PIGMENTS OF CCELENTERA 93 
benzol, chloroform, phenol, heat, etc., destroy the blue 
colour and give a precipitate of dull red or brown 
colour. The blue solution in water gives three (or 
two ?) bands in its spectrum, but Professor E. R. 
Lankester (1870) did not succeed in getting these 
bands with Vellela; the reddish-brown substance 
apparently gives no bands. Further, in Rhizostoma 
Cuvieri the blue colour is somewhat variable; it 
chiefly occurs in young specimens; the older, especially 
when carrying eggs, are of dirty red or reddish-brown 
tint. This must surely be due to the modification of 
the unstable blue pigment under the influence of 
some specific change in the chemical characters of the 
protoplasm of the organism. Then again, Professor 
M'Kendrick found that the brown colouring-matter of 
the jelly-fish Chrysaora was soluble in hot sea-water, 
yielding a dark brown solution of acid reaction, which 
gave a reddish-brown precipitate with strong alkali. 
It seems probable that this colouring-matter is also 
the result of a modification of cyanein. 
These cases show that in all probability the 
number and variety of the tints in the Ccelentera 
are due in large part to physical or chemical changes 
in a few complex pigments. As to the cause of these 
changes, it must be noted that the pigments are here 
deposited in internal structures where active meta¬ 
bolism is going on, and not, as in many higher 
animals, in superficial inert tissues. The physiology 
of the higher Vertebrates shows that in them there is 
a metabolism of pigment as active as any that can 
occur in coral polypes ; but while in the latter every 
change is apparent on the surface, in the former the 
changes are concealed by the intervening passive 
