IV THE COLOURS AND PIGMENTS OF PROTOZOA 77 
As to the pigment itself, according to Johnson 
it normally varies in tone from bright sky-blue to 
pale sea-green or even dull bluish-gray, but if the 
organisms are kept under unfavourable conditions 
it becomes reduced in quantity and changes to 
a yellowish-brown colour. This change always 
occurred when the Stentors were artificially divided, 
and Johnson never found the blue colour to be 
regained when once lost—a curious fact (the 
statement, of course, refers to forms kept in con¬ 
finement). Individuals are sometimes found which 
are almost devoid of pigment. Schuberg observed 
a fact confirmed by Johnson that the pigment is 
thrown out of the living Stentors apparently in the 
same way as that in which faecal matter is got 
rid of; the pigment tends especially to accumulate 
near the point of attachment in forms which have 
remained long in one place. 
The blue pigment is extremely stable, not being 
dissolved by alcohol, ether, etc., nor attacked by 
acids or alkalies. 
Another Protozoan ( Nassula ) also contains a 
blue pigment which is probably derived from the 
Oscillatoria of the food. 
Another beautiful violet pigment, apparently of 
unknown characters, is described by Dr. O. Niisslin 
in a Protozoan (Zoonomyxa violacea ) found in the 
Herrenwieser Lake. This organism has its proto¬ 
plasm filled with numerous small violet vacuoles, 
sufficiently abundant to colour the whole organism 
violet. The pigment has a superficial resemblance 
to one described by Greeff in Amphizonella violacea , 
but in that form the pigment is granular, while here 
