76 
COLOUR IN NATURE 
CHAP. 
many of the colouring-matters of the Protozoa are 
as adventitious and unimportant as these, but of the 
physiology of the Protozoa relatively little is known. 
Apart from the lipochrome pigments and chloro¬ 
phyll we find that, as already seen, blue and violet 
pigments are not uncommon in the Protozoa. In 
Stentor ccernleus notably, the presence of a blue pig¬ 
ment in the alveolar layer has long been known. 
According to Biitschli the pigment may be blue, 
red, rusty-yellow, or coffee-brown. It was examined 
spectroscopically in 1873 by Prof. E. Ray Lankester, 
who found that it gave a three-banded spectrum. 
More recently it has been again investigated by 
Mr. Herbert Johnson, who has made a special study 
of the American species of Stentor. 
In several of these chlorophyll is present in the 
form of the so-called zoo-chlorellae, but these are 
entirely absent from .S', cceruleus, which is the largest 
form and the one which is hardiest in aquaria. In 
it there is abundant pigment present in the ectoplasm, 
the pigment being arranged in stripes which corre¬ 
spond to ribs or stripes in the ectoplasm. The stripes 
are very inconspicuous in species in which pigment 
is absent, but can be demonstrated in these by 
differential staining. The occurrence of pigment in 
these simple organisms showing a differential dis¬ 
tribution associated with morphological differences 
in structure and physiological differences in reaction 
to chemical agents, is a fact of much theoretic interest. 
It will be noted that the result of the differential 
distribution is to produce a simple form of marking 
—a true coloration in the common use of the 
term. 
