II 
THE PIGMENTS OF ORGANISMS 
4i 
said to be obtained from the diatoms of their food, 
used to be given as an example ; another is the case 
worked out recently by Mr. Poulton (1893), showing 
that the green pigment of some caterpillars is derived 
from the green leaves upon which they live. Another 
example, which in some degree resembles Mr. 
Poulton’s case, is one mentioned by Zopf (1892). In 
studying the colouring-matter of the fungus Pilobolus 
already mentioned, he found that a parasite growing 
on the fungus took up not only the drops of oil but 
also the pigment associated with the oil, the result 
being that parasite and host were similarly coloured. 
This is interesting, because it probably has some 
bearing on certain of the cases of colour-resemblance 
which are now so numerous in the literature of colour. 
The above five sets of pigments have been con¬ 
sidered in some detail, because it is quite possible 
that ultimately the greater number of the pigments 
at present known may be found to fall into one or 
other of these categories. In the meantime, however, 
there is no proof of this, and there are very many 
pigments which it is quite impossible to classify. On 
this account, we shall simply consider them system¬ 
atically under the organisms in which they occur. 
Before doing this it may be well, in the absence 
of a complete classification of pigments , to consider 
for a little the distribution of pigmental colours in 
organisms. 
The Distribution of Pigmental Colours 
Bluets a pigmentalcolourisexceedinglyrare among 
the more complex animals, but is not uncommon among 
