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 



