30 MANUAL OF ANIMAL BIOLOGY 



fluid ectoplasm in a constant shape. The cell wall, however, is 

 sufficient to maintain a regular body outline so that protruding 

 pseudopodia are not formed as in the Amoeba. (B. p. 35.) 



Projecting from the somewhat blunt anterior end of Euglena 

 is a delicate, vibratile filament, or flagellum. 1 This structure 

 arises from a number of very fine fibrils present in the ectoplasm 

 near the anterior end of the body, which are united to form the 

 flagellum. The flagellum is attached in a depression, or pit, in 

 the ectoplasm. In some of the Protozoa this pit extends down into 

 the endoplasm and serves as a passage for food particles. In 

 Euglena, however, it apparently has nothing to do with the process 

 of obtaining food, but serves as a canal for the passage of fluids 

 from the contractile vacuole system. In an active individual the 

 flagellum is continually vibrating with such great rapidity that it is 

 difficult to see. It serves as an organ of locomotion and, as a 

 result of its spiral movement, the organism is drawn ahead with 

 considerable speed. (W. f. 22.) 



The endoplasm of Euglena, which makes up the greater part 

 of the animal, contains a number of interesting structures. At the 

 anterior end, just back of the so-called gullet, is the contractile 

 vacuole. This structure does not have the simplicity that charac- 

 terized the single contractile vacuole of Amoeba. It consists of a 

 large central reservoir which is believed to empty into the gullet. 

 Around the edge of it are several tiny contractile vacuoles which 

 discharge the liquid wastes into the central reservoir. 



Situated close to the reservoir of the contractile vacuoles is a 

 spherical body of great interest, known as the eye spot, or stigma, 

 which consists of a tiny bit of cytoplasm containing reddish-colored 

 pigment (hematochrome) . It is believed that the stigma is a 

 primitive type of light-receiving apparatus since it is known that 

 this region is sensitive to light rays. This enables Euglena to find 

 the place in its environment which is best adapted for its photo- 

 synthetic nutritive processes. (W. f. 22.) 



The chlorophyll in Euglena is contained in disc-shaped chro- 

 matophores scattered through the endoplasm. Pyrenoids, 

 which probably serve as starch-forming centers, can also be dem- 

 onstrated in some individuals. 



The comparatively large nucleus of Euglena lies embedded in the 

 endoplasm, just posterior to the center of the animal. 



1 Plural, flagella. 



