240 



COMPARATIVE ZOOLOGY. 



the essential signs of life. The usual methods of repro 

 duction are self-division and budding. 



The snbkingdoin may be divided into four classes: 

 nera, Rhizopoda, Gregarinida, and Infusoria. 



CLASS I. Monera. 



These simplest living beings are organless 

 bits of protoplasma, with no distinction of lay- 

 ers, and so far as observed not even a nucleus 

 is present. They are round when at rest, and 

 have pseudopodia when active. They are all 

 aquatic, and some are parasitic. Such is Pro- 

 tamoeba, Fig. 183. 



CLASS II. Rhizopoda. 



The Rhizopods are characterized by the power of throw- 

 ing out at will delicate processes of their bodies, called 

 pseudopodia, or false feet, for prehension or locomotion. 

 They possess no cilia. The representative forms are Amosr 

 bee, Foraminifera, and Radiolaria. 



An Amoeba is a naked fresh-water Rhizopod ; an in- 

 definite bit of protoplasm, as structureless as a speck of 

 jelly, save that it is made of 

 two rather distinct layers, and 

 has a nucleus and a contractile 

 cavity inside. It thus differs 

 from the Monera. It has no 

 particular form, as it changes 

 continually. It moves by put- 



ting forth Short, bllint prOC- 



esses, and eats by wrapping 

 its body around the particle of food. The size ranges 

 from -7^ to u-gVo- f an inch in diameter. Specimens can 

 be obtained by scraping the slimy matter from the stems 

 and leaves in stagnant ponds. 



m.- Amoeba princeps, X 150; the 



Bame animal iu various 8hapes ' 



