OTHER PROTOZOA 85 



pyrenoids. Both the pyrenoids and chromatophores are perma- 

 nent cell structures and increase in number by division and not by 

 the origin of new ones from the other parts of the body. 



Locomotion. Euglena changes its shape frequently, becom- 

 ing shorter and thicker, and shows certain squirming movements. 

 These prove that it possesses considerable elasticity, since the nor- 

 mal shape is regained if enough water is present. Often in a 

 favorable specimen, a thread-like structure may be seen project- 

 ing from the anterior end of the body and bending to and fro, 

 drawing the animal after it. This is the flagellum. It arises from 

 a number of branching root-like fibrils within the body, passes 

 through the wall of the mouth depression, and extends forward to 

 a distance often equal to the length of the animal. The part of the 

 flagellum outside of the body is composed of four contractile 

 fibrils which are wound together spirally (Fig. 25). The con- 

 traction of these fibrils is supposed to produce all of the move- 

 ments characteristic of this structure (56). If the flagellum 

 cannot be seen in the living animal, a little iodine placed under 

 the cover glass will help to bring it out. 



Nutrition. Although Euglena has a mouth and gullet, it is 

 very doubtful if any food is taken in. Food is manufactured as 

 in green plants, by the aid of the chlorophyll in the chromato- 

 phores. This mode of nutrition is known as holophytic. That all 

 the food necessary for the life of the animal is not procured in this 

 way is shown by the fact that the animal is able to live in the da'rk 

 for over a month, whereas chlorophyll demands light before the 

 production of paramylum is possible. This seems to indicate 

 that organic substances in solution are absorbed through the 

 surface of the body, that is, saprophytic nutrition supplements the 

 holophytic. The nutrition of Euglena differs from that of the 

 majority of animals, since the latter live by ingesting solid par- 

 ticles of food and are said to be holozoic. 



Encystment. Occasionally Euglena are found which have 

 become almost spherical and are surrounded by a rather thick 



latinous covering which they have secreted. Such an animal 



