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 



