74 
COLOUR IN NATURE 
CHAP. 
—an interesting fact, because this association or lipo- 
chromes in pairs is widely spread throughout both 
the animal and vegetable kingdoms. In Euglena 
sanguinea the colouring-matter may be absent with¬ 
out apparently any resulting specific difference. The 
red colour occurs chiefly in spring, in autumn, in the 
dry condition and in bright sunshine, a state of 
affairs quite comparable to that which obtains in the 
higher plants. According to Engelmann (1882), the 
red colouring-matter is capable of evolving oxygen 
as well as the green. 
Among other Protozoa which do not contain 
chlorophyll, red pigments sometimes occur, often 
being found only in the so-called eye-spots. In 
mass the red colouring-matter may sometimes render 
the tiny organisms very conspicuous ; thus Agassiz 
speaks of Globigerina occurring in floating masses of 
scarlet colour, and forming an appreciable factor in 
the coloration of the ocean-surface. 
A brown colouring-matter, perhaps identical with 
the pigment of Diatoms (diatomin), seems to have 
a wide distribution among the Protozoa, but the 
question whether it is an intrinsic or a derived pig¬ 
ment is as yet undetermined. It occurs occasionally 
in the cortical layer of Vorticella for example. 
Among the Protozoa containing chlorophyll or 
lipochromes we must also mention the Radiolaria. 
Many of these contain the so-called yellow cells, 
which are little masses of protoplasm apparently 
coloured by chlorophyll, plus some other pigment. 
There is strong evidence in support of the conclusion 
that these are unicellular algae living in symbiosis 
with the Radiolarians (Geddes, Brandt). Others 
