CHAPTER VII 



PHYLUM PROTOZOA— THE SIMPLEST 



ANLMALS 



Chief Divisions 



Rhizqpods : Classes — Lobosa, Heliozoa, Foraminifera, Radio- 



LARIA, etc. 



Infusorians : Classes — Flagellata, Ciliata, Acinetaria, etc. 

 Sporozoa : Several Classes. 



The Protozoa are the simplest animals, and they are of 

 pecuhar interest on this account. They throw light upon 

 the beginnings of organic structure and vital activity, and 

 they give us hints as to the nature of the first forms of life, 

 of which we can know nothing directly. Almost all the 

 Protozoa are single cells, iinit masses of living matter ; and 

 in virtue of their simpUcity, they are in some measure 

 exempt from natural death, which is " the price paid for a 

 body." In their variety they exhibit, as it were, a natural 

 analysis of the higher animals, w^hich are built up of many 

 diverse cells. 



General Characters 



The Protozoa^ the simplest and -most primitive animals, 

 are usually very small single cells. Most of them feed on 

 small plants or on other Protozoa, or on debris, and not a 

 few are parasitic. Most of them live in water, hut many can 

 endure dryness for some time. In one series (Rhizopods) 

 the living matter is without any rind, and flows out in more 

 or less changeful threads and lobes, by the movements of which 



the animals engulf their food and glide along. The others 



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