240 



COMPARATIVE ZOOLOGY. 



the essential signs of life. The usual methods of repro- 

 duction are self-division and budding. 



The subkingdom may be divided into four classes: Mo- 

 nera, Rhisopoda, 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 

 ^tamoeiapri- aquatic, and some are parasitic. Such is Pro- 

 tamoeba, Fig. 183. 



mitiva. 



Class II. — Rhizopoda. 



The Khizopods 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 Amos- 

 bcB, Foraminifera, and Radiolaria. 



An Amoeba is a naked fresh-water Rliizopod ; 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, blunt proc- 

 esses, and eats by wrapping 

 its body around the particle of food. The size ranges 

 from T,V to a 8*6 ft of an inch in diameter. Specimens can 

 be obtained by scraping the slimy matter from the stems 

 and leaves in stagnant ponds. 



Via.TSi.—AmKba pHruxps, X 150; the 

 eame animal in varione shapes. 



