AMCEBA AND SOME ALLIES: PROTOZOA 283 



Under certain conditions of the environment the amoeba 

 ceases moving about; it takes on the form of a ball, and 

 incloses itself in a membrane or cyst. The encysted amoeba 

 remains in that state until the return of favorable conditions 

 in its habitat. 



Euglena. A relative of Amoeba, found in the same situ- 

 ations, is Eugle'na vir'idis (Fig. 141) ; it also is composed of 

 one cell. Euglena has a more fixed arrangement of parts 

 than Amoeba. There is a blunt anterior end with a short, 

 funnel-shaped mouth to carry food into the cytoplasm. Out 

 of the mouth extends a long lash, which by its whip-like 

 vibrations carries the animal through the water, and at 

 the same time sends food back to the mouth. Behind the 

 mouth is a small red eye-spot, which lies beside a clear 

 space. This clear space has been found to be sensitive to 

 light. The nucleus is near the middle of the body, and 

 can be seen easily in the living animal, although 

 the cytoplasm immediately about it is colored 

 quite green with 

 chlorophyll, a 

 coloring matter 

 found in the 



green parts of FlG 141 Euglena. Much enlarged. (After Saville Kent) 

 plants. 



Many biologists believe that Euglena is indeed a plant 

 because, through the agency of its chlorophyll, it can use car- 

 bon dioxide as a raw food-material, retaining the carbon and 

 giving off oxygen when the organism is in the light. This 

 creature illustrates the fact that it is impossible to classify 

 all organisms as plants or animals. 



As a rule Euglena moves with the lash forward, but the 

 animal can turn in any direction, and can even change 

 the shape of its body considerably, but it does not form 

 pseudopodia. Sometimes when being experimented 011 with 



