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according to environment, and are therefore properly 

 termed mixotrophic organisms. Certain Flagellates, notably 

 Mastigamceba, are amoeboid at one period and flagellate 

 at another. Some have siliceous shells. There are fresh- 

 water and marine forms. A number are free-living (e.g., 

 Euglena, Volvox which forms colonies, and the marine 

 Noctiluca which lives at the surface of the sea), and many 

 are parasitic (e.g., Copromonas) and pathogenic, causing 

 disease (e.g., Trypanosomes). 



Their general mode of reproduction is asexual, by longi- 

 tudinal fission ; but a sexual process (formation of gametes 

 followed by conjugation) is also frequent. 



Give a short Description of Euglena. 



EUGLENA swarms in ditches and puddles, often in pro- 

 fusion, forming a green scum on the surface. It is minute 

 in size and elongate in shape, pointed at one end and 

 blunt at the other. At the blunt end is a tiny opening, 

 the funnel, and a long flagellum arises from its wall inside. 

 Acting like a ship propeller, but in a spiral way, the flag- 

 ellum pulls Euglena swiftly along. At times it slows down 

 and goes through curious changes of form swells out in 

 the middle, rounds itself off, becomes oval, bends, and so 

 on expressive of a very elastic cuticle, and all so peculiarly 

 characteristic that they are termed " euglenoid." These 

 changes are effected by the contractile myoneme fibrils 

 of the ectoplasm. Not clearly visible, except when stained, 

 is the nucleus in the middle of the body. Beside the funnel 

 is the clear reservoir into which several small contractile 

 vacuoles discharge. On the side of the reservoir is a small 

 red spot (the stigma) sensitive to light. Throughout the 

 endoplasm there are green chromatophores and grains of 

 paramylum, a substance allied to starch, formed by de- 

 composing carbonic acid through the action of the chrom- 

 atophores. Euglena multiplies by longitudinal binary 

 fission, and it also encysts, undergoing successive longi- 

 tudinal divisions. 



