CHAPTER IX 



ORDER 5 EUGLENOIDIDA BLOCHMANN 



THE EUGLENOIDIDA include many of the large flagellates of 

 common occurrence. Some are plastic, but others have a 

 definite body form with a well-developed, striated or variously 

 sculptured pellicle. The body is usually elongated. At the 

 anterior end, there is an opening through which a flagellum 

 protrudes. In holophytic forms the so-called cytostome and the 

 cytopharynx, if present, are apparently not concerned with 

 food-taking, but seem to give a passage-way for the flagellum 

 and also to excrete the waste fluid matters which become col- 

 lected in the contractile vacuoles located around the reservoir. 

 In holozoic forms, a well-developed cytostome and cyto- 

 pharynx are present. The contractile vacuoles form a complex 

 structure and are highly characteristic of the group. There are 

 several minute contractile vacuoles arranged around a reservoir 

 which receives their contents, and discharges through the so- 

 called cytopharynx. Ordinarily there is only one flagellum, but 

 two or three are present in a few forms. Chromatophores are 

 present only in Euglenidae and absent in the other two families. 

 They are green and of various shapes, such as spheroidal, 

 band-form, cup-form, discoid, or stellate. They usually con- 

 tain pyrenoids. Some forms may contain haematochrome. A 

 small but conspicuous stigma is invariably present near the 

 anterior end of the body in chromatophore-bearing forms. 



Reserve food material is the paramylum, the presence of 

 which depends naturally on the metabolic condition of the or- 

 ganism. The paramylum body assumes diverse forms in differ- 

 ent species, but is constant in each species, and this facilitates 

 identification to a certain extent. Nutrition is holophytic in 

 chromatophore-possessing forms, which, however, may be sap- 

 rozoic, depending on the organic substances present in the water. 

 The holozoic forms feed upon bacteria, algae and smaller Pro- 

 tozoa. 



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