II 
THE PIGMENTS OF ORGANISMS 
47 
surface forms, but attains its greatest brilliancy 
among those inhabiting deep water, which often 
exhibit a wonderfully pure and bright scarlet tint. 
All these red tints are due to lipochromes. The red 
blood-pigment haemoglobin is frequently important in 
coloration in simple forms, especially worms, but the 
effect is produced by the shining through of the 
red blood, and not by the deposition of haemoglobin 
as a superficial pigment In butterflies red pigments 
important in coloration occur which are probably 
modified waste products. Among plants red pig¬ 
ments are probably usually either lipochromes or 
anthocyans ; red is an exceedingly common colour 
among plants. 
Black and deep brown pigments are very widely 
distributed in the more complex animals, and are 
virtually absent from plants and simple animals. 
As exceptions we may note the presence of a brown 
pigment in Hydra fusca and the “ brown body ” of 
Polyzoa. The former, according to Miss Greenwood, 
is a waste substance, the latter will be discussed 
under Polyzoa. That their distribution is not wholly 
dependent upon structure is, however, shown by the 
fact that they are rare in Crustacea and exceedingly 
common in Insecta, slightly developed in most 
Chaetopoda and often marked in Hirudinea. There 
is some evidence to show that they do not commonly 
occur in connection with structures containing car¬ 
bonate of lime, which may serve to explain their 
rarity in Crustacea. At least it is noticeable that in 
Mollusca very dark brown or black pigments do not 
usually occur in the shells, while they may be common 
in the mantle, internal organs, or secretions, as in 
