374 



GENERAL ZOOLOGY 



An amoeba is protected to a certain extent by its ectoplasm, 

 which has the characteristics of a thin elastic membrane; but 

 since it often overcomes its enemies, if small enough, by 

 engulfing them, securing food and gaining protection are in 

 such cases accomplished by the same operation. 



Amoeba proteus reproduces by simple fission, during which 

 an intranuclear spindle and chromosomes are formed. Accord- 

 ing to some observations the nuclear membrane persists 



.*•:•.*■ .-.. . v .1 ■ m *>v ... • ■ . '.. ' . •■■*..■ f 



u 





£/ 



ill 





B 



Fig. 208. — Reactions of Amoeba proteus to food. A, ingesting a portion of 

 nonmotile bacterial glea; B, ingesting a Paramecium, which has been constricted 

 into a dumbbell shape. (After Kepner and Whitlock.) 



throughout the mitotic process, surrounding the spindle. 



During the telophase it constricts into two parts, within each 



of which nuclear reorganization then follows. 

 Order 2. Proteomyxa. Protozoa with filamentous and often 



branching pseudopodia. 



Example: Nuclearia simplex, common on Spirogyra and 



other fresh-water plants. 

 Order 3. Testacea. Body enclosed in a single-chambered shell 



provided with a single opening through which the pseudopodia 



can be thrust. 



Example: Difflugia urceolata, a fresh-water form (Fig. 209). 



