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 cceruleus notably, the presence of a blue pig- 

 ment in the alveolar layer has long been known. 

 According to Butschli 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 5. 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. 



