40 



FLAGELLATE PROTOZOA 



to that in other Protozoa and is not, as it has been described, 

 specially comphcated. A red pigment spot or stigma Hes 

 against the front side of the reservoir and enables the working 

 of the flagellum to be regulated by the amount of light in the 



Fig. 15. — Euglena viridis. 

 A, B, C, Three postures of the body. 



surroundings. Reproduction is by binary fission, beginning at 

 the front end, the nucleus undergoing a peculiar mitosis. It may 

 take place in free individuals after the loss of the flagellum, or 

 in a gelatinous cyst, within which it may be repeated several 

 times. The occurrence of syngamy is extremely doubtful. Our 

 knowledge of the nutrition of Euglena is too confused and compli- 



flagellum 



gullet 



eyes pot 



contractile vacuole 



Fig. 16. — stages in the formation and discharge of the contractile vacuole in 

 Phacus, a flagellate related to Euglena. — Modified from Hyman. The 

 Invertebrates: Protozoa through Ctenophora, by kind permission of McGraw- 

 Hill Book Company. 



cated to be summarised in an elementary book. It is doubtful 

 if E. viridis can feed in an entirely plant-like manner, though 

 E. gracilis can. All species can grow if they are in the light, 

 provided that a suitable source of organic nitrogen be present, 

 and many can also grow in the dark if organic carbon and nitrogen 

 be available ; under these circumstances the chloroplasts lose 

 their green colour. 



