156 ORGANISMS ILLUSTRATING BIOLOGICAL PRINCIPLES 



pspiidopodia are relatively small. After the nucleus divides, the cell 

 body separates into two equal parts, each of which grows into a 

 full-sized individual. 



Euglena 



Although Ameba is usually looked upon as the simplest of all animal 

 cells, there is another group of organisms containing equally simple 



forms, making up a large 



flagsllum 

 cytostome/. 



stigma .^^<a. 



I^lagsllcu- granule 



rs-Ser-vDirr 



basal granule 



Contractile, 

 vacuoles -•'- 



nuole-us — 



Central bcx^ 



cbromatopbore 

 pyrenoid 



striation$ — 



lent 



Euglena viridis. Read your text and give 

 the functions of each of the structures shown. 

 Note that the drawing makes the cell appear 

 flat whereas in cross section it is oval. What 

 evidence of holophytic nutrition is seen in 

 this diagram ? (After Hegner.) 



proportion of the microscopic 

 plankton of the ocean and 

 bodies of fresh water. This 

 grotip, w^hich comprises one 

 of the classes of the Phylum 

 Protozoa, includes the Masti- . 

 gophora, or flagellates, cells 

 that move by means of one or 

 more long, whiplash threads 

 of protoplasm. Certain of 

 the Mastigophora bear a close 

 relationship to plants, and the 

 organism Euglena, selected as 

 a representative of the group, 

 is often claimed as a plant cell 

 by botanists. Euglena may 

 be found in shallow and some- 

 times temporary freshwater 

 ponds, where it often grows 

 with such rapidity as to give 

 a dull greenish color to the 

 water. When unfavorable 

 conditions set in, the organism 

 settles to the bottom, becomes 

 covered with a resistant coat 



or cyst, and is only recalled 

 to active life by a recurrence of favorable environmental conditions. 

 Some species of Euglena have conspicuous spiral markings on the 

 surface of the body, which is roughly ovoid, with a depression at the 

 anterior end, called the gullet. A single flagellum has its origin near 

 the base of the gullet, in the form of a long axial filament anchored 

 in the protoplasm, that gives the filament free movement. By 



