188 THE PROTOZOA 



(a) Holophytic Nutrition. The characteristic of this type of 

 nutrition is that the organism contains special pigments by means 

 of which it is able to decompose CO 2 in the sunlight, setting free 

 the oxygen and retaining the carbon, which is built up in union 

 with other elements derived from water and mineral inorganic salts. 

 The pigments, termed comprehensively chromophyll, are contained 

 in bodies termed " chromatophores," which occur in diverse forms 

 and varying numbers in different species, and which multiply by 

 division when the cell divides. The chromophyll-pigments are of 

 various tints -- yellow, brown, green, blue-green, etc.- -but the 

 commonest tint is the green chlorophyll, similar to that character- 

 istic of plant-cells. A blood-red pigment, termed hcematochrome, 

 occurs in some flagellates e.g., Hcematococcus ; it appears to be a 

 modification of chlorophyll produced under certain conditions (see 

 Reichenow, 97*5). 



For the details of the complicated process of the synthesis of 

 chemical substances in the holophytic mode of nutrition, the student 

 is referred to botanical textbooks dealing with plant-physiology. 

 There appears to be no essential difference between the assimilative 

 processes of holophytic Protozoa and of ordinary plant-cells. A 

 characteristic product of holophytic nutrition is seen in the forma- 

 tion of amyloid substances, the most important of which are starch 

 (amylum), and an allied substance known as " paramylum," which 

 differs from starch in some of its reactions, notably in that it is not 

 coloured blue with iodine. Paramylum is of more frequent occur- 

 rence in Protozoa than true starch. The amyloid substances occur in 

 characteristic masses in the cytoplasm (see especially Butschli, 153). 



The chromatophores of Protozoa contain usually small refringent 

 bodies termed pyrenoids, which also multiply by division. The 

 pyrenoids are often surrounded by a coat or envelope of paramylum, 

 and appear to be the centres of the production of amyloid substance. 



Many flagellates with green chromatophores combine holophytic with 

 saprophytic nutrition. Examples of such " mixotrophic ' forms are seen 

 in the genus Euglena (Zurnstein, 223), the species of which flourish best in 

 a medium containing organic substances, and cannot maintain themselves 

 in pure water. Euglena viridis was shown by Khawkine to be able to live 

 for a considerable period in the dark in media containing organic substances, 

 but did not lose its green colour and did not multiply. E. gracilis, on the 

 other hand, in Zumstein's experiments, lost its green colour and passed into 

 an Astasia-]ikQ phase in the dark, or even in the light when placed in solutions 

 very rich in organic substances, nourishing itself as a saprophyte. When the 

 Astasia-iorm was exposed to the light, in solutions containing a small amount 

 of organic matter, it became green again and passed back into the Euglena- 

 phase. The degree to which the species of Euglena can adapt themselves 

 to a purely saprophytic life would appear to vary in different cases. In the 

 colourless forms the chromatophores lose their chlorophyll, and remain as 

 colourless leucoplasts. 



The combination of holozoic and holophytic nutrition has been rioted 

 above (p, 15). 



