PROTOZOA 37 



important. Others, as Euglena viridis, bleach in the absence of Hght, 

 but can still flourish if the presence of organic matter in solution makes 

 saprophytic nutrition possible. Holozoic species must of course have 

 their proper food ; in infusions they appear as this becomes plentiful, 

 first, after the bacteria, those whose diet is purely bacterial, such as 

 Monas and Colpoda, then those, such as Stylonichia, that feed upon the 

 first comers, and so on ; though some bacterial feeders, as Paramecium ^ 

 are rather late to appear. Temperature has also an influence upon 

 c.vac. 



f.vac 



Fig. 33. Actinosphaerium eichhornt, x 180, From Leidy. The endoplasm is 

 crowded with food vacuoles containing diatoms, and nuclei are represented 

 in the figure by the dark areas, c.vac. contractile vacuole ;/.z;ac. food vacuole 

 which has just swallowed a rotifer; ps. pseudopodia. 



protozoan faunas. The powers, possessed by freshwater protozoa, of 

 distribution across inhospitable regions and of surviving unfavourable 

 conditions at home are no doubt due to the facility with which they 

 form resistant cysts (p. 16). In various cases all the unsuitable con- 

 ditions of the environment indicated above have been found to induce 

 encystment, and encysted protozoa have been discovered in dust from 

 the most remote desert regions. 



The protozoa which live in dung {coprozoic species) and in decaying 



