298 
COLOUR IN NATURE 
CHAP. 
Most have been conducted by the method of sections, 
and during the course of preparation of the objects, 
the lipochromes, and the numerous other unstable or 
soluble pigments, are completely removed or destroyed, 
so that of these the investigators have nothing to 
say. It is obvious, however, that it is these brightly 
coloured substances which give rise to the most 
striking of the phenomena of coloration. Practically 
any substance occurring in opaque granules may give 
rise to dull brownish colours, and so may be termed 
a pigment, but does this help us as to the origin of 
the bright blue of many jelly-fish, the gorgeous red 
of some Crustacea, the bright colours of fishes and 
birds ? These may be “ waste products,” but there 
is yet no proof of it; they may be reserves; they may 
be comparable to the production of aniline dyes in 
the coal-gas industry, i.e. by-products (Durham), but 
there is as yet little certainty. It is possible that 
some of the difficulties may be solved by a careful 
study of the chaetopterin group of pigments, for the 
members of it are widely distributed, tend to occur 
in connection with endodermic (digestive) organs, and 
under artificial conditions give rise to brightly coloured 
derivatives, but the investigations have still to be 
made. 
Again, the method of study by means of injec¬ 
tions has obviously its limitations as a method of 
determining the physiological value of pigments. 
Thus Cuenot found that introduced pigments in the 
case of the Crustacea were eliminated by the excre¬ 
tory organs, or by the hepatic cells and the faeces ; 
they were never stored up in the epidermal tissues, 
and yet the Crustacea are remarkable for the pro- 
