II 
THE PIGMENTS OF ORGANISMS 
45 
therefore only in rare cases of direct importance in 
coloration. Of this group, “ enterochlorophyll,” 
bonellin, and chaetopterin are good examples ; the 
two latter give rise to external coloration in the 
forms in which they occur. We shall make frequent 
reference to these pigments in the course of the 
following chapters. 
The occurrence of green colour in organisms from 
which yellow lipochromes only can be extracted is 
an exceedingly common phenomenon, which has been 
observed in many different animals. The green 
colour is doubtless due in many cases to the structure 
of the coloured parts ; in others it may be due to a 
combination of the lipochrome with a base ; there is 
little doubt that the green colour of many Crustacea 
is in part due to this cause. Apart from chlorophyll 
and lipochrome combinations, green pigments occur 
freely in many Coelentera, in many worms, and in 
some Mollusca; in these cases they are usually soluble 
in alcohol and often give banded spectra, but most 
have been very imperfectly investigated. In Verte¬ 
brates green pigments are almost absent; as in the 
case of blue pigments, the most marked exception is 
probably the green pigment which colours birds’ eggs, 
though according to Sorby the green colour is here 
produced by a mixture of blue and yellow. As a 
colour, green in animals is most abundant among 
those inhabiting trees or herbage, but is here very 
frequently structural. In marine animals it seems to 
occur in large masses chiefly in coral-reefs, where the 
corals are often largely green. In these situations 
green plants are relatively rare, and accordingly the 
green colouring-matter has been supposed by Dr. 
