PHYLUM PROTOZOA 43 



Anatomy. - - Euglena (Fig. 22) is a simple elongated cell, and, 

 although somewhat elastic, maintains a more or less constant 

 shape. It possesses, in addition to ectosarc and endosarc, a thin 

 outer membrane, the cuticle, which is striated, as shown in Figure 

 22, B. Near the center of the anterior end is a long slender 

 whiplike process, iheflagellum, which extends out from an open- 

 ing called the mouth (Fig. 22, A, m). From the mouth a tubular 

 " gullet" leads to a permanent vesicle, the reservoir (A, r); into 

 this reservoir several contractile vacuoles (A, cv) discharge their 

 contents. Close to the reservoir is a protoplasmic mass con- 

 taining granules of a red coloring matter, hamatochrome ; this 

 is called the stigma or eye-spot (A, e) because it is supposed to be 

 especially sensitive to light. Near the center of the body is 

 a nucleus (A, n}, and scattered about in the protoplasm are many 

 oval bodies, greenish in color, called chromatophores (A, ckr). 



Physiology. - - NUTRITION. - - Euglena probably does not 

 ingest solid particles by means of the mouth and gullet, but 

 manufactures its own food by the aid of the chlorophyll contained 

 in the chromatophores. As in plants, this chlorophyll is able, 

 in the presence of light, to break down the carbon dioxide (C0 2 ), 

 thus setting free the oxygen, and to unite the carbon with water, 

 forming a substance allied to starch, called paramylum (Fig. 22, 

 A and B, am}. This mode of nutrition is known as holophytic. 

 Some organic substances are probably absorbed through the 

 surface of the body, that is, saprophytic nutrition supplements 

 the holophytic. Euglena differs from most animals in its method 

 of nutrition, since the majority of them ingest solid particles and 

 are said to be holozoic. 



Behaviour. - - LOCOMOTION. - - Euglena because of its elastic- 

 ity is able to squirm through small openings, but its chief method 

 of locomotion is swimming. The flagellum, consisting of four 

 contractile fibrils which are wound together spirally, bends to 

 and fro, drawing the animal along. 



REACTIONS TO STIMULI. - - Euglena is very sensitive to light, 

 and is a favorable object for the study of phototropism. It 



