90 



Occurrence of Microorganisms in Soil 



Fig. 43. Flagel- 

 late, Bodo cauda- 

 ttis ( from Martin 

 and Lewin). 



nucleoproteins. In addition to these, carbohydrates, Hpoids, and 

 enzymes are always present in the hving cell. Also found in the 

 protozoa are undigested food particles, waste materials, or foreign 

 elements, which take no part in the physiology of 

 the organism; algae and bacteria may often be 

 present in the endoplasm, either as ingested food 

 or as a result of a certain symbiotic relationship. 

 Many species of protozoa are subject to attacks by 

 parasitic organisms. 



The protozoa are classified on the basis of loco- 

 motion, as follows: 



1. Sarcodina or Rhizopoda. Motility by means 

 of pseudopodia, which are extensions of the proto- 

 plasm of the cell body. The pseudopodia are 

 broad, blunt, finger-like or filiform, simple, or 

 branched. In some, the ray-like pseudopodia are 

 usually supported by axial filaments. Some of the 

 rhizopods are naked. Others form shells, which 

 are composed of secreted materials, as chitin, 

 silica, and calcium carbonate; they may also be constructed from 

 foreign materials, as diatoms, sand grains, and clay particles. Some 

 shells are delicate, transparent, whereas others are composed of dis- 

 tinct plates, arranged more or less regularly. 



2. Mastigophora or Flagellata. Motility by means of flagella. 

 These flexible whip-like processes are usually 



attached at one end of the body. Either one 

 or more flagella may be present. When single, 

 the flagellum is usually directed forward and 

 draws the body forward by its movement. 

 When more than one flagellum is present, one 

 or more may be directed backward. Some 

 low flagellates can form pseudopodia. 



3. CiUata or Infusoria. Motility by means 

 of numerous cilia or short hair-like processes 

 present during the entire existence of the 

 protozoa or during their embryonic stage only. 

 The cilia are either evenly distributed over 

 the surface of the organisms or restricted to 

 certain regions. Large spine-like cirri or setae, or vibrating mem- 

 branelles, may be formed from fusion of cilia. Most ciliatcs are free 

 swimming; some are attached by rigid or flexible stalks or pedicels. 







«» 





V 



Fig. 44. Ciliate, Col- 



poda steinii ( from 



Goodey ) . 



