354 BIOLOGY OF THE PROTOZOA 



describes no less than 250 species capable of living in the soil. 

 With arable soils the maximum numbers are found, as a rule, at a 

 depth of 4 to 5 inches while the sub-soil is generally free from 

 them. Such soil-dwelling types are able to live under partial 

 anaerobic conditions and are usually bacteria-eating holozoic forms. 

 As such they become important factors in all economic matters 

 concerning soil productiveness. 



Of the flagellate group Sandon describes seven species which seem 

 to be limited to this habitat (Allantion trachyploon, Sandon; Alias 

 diplophysa, Sandon; Colponema symmetrica, Sandon; Phalansterium 

 solitarium, Sandon; Sainouron mikroteron, Sandon; Tetramitus spir- 

 alis, Goodey; Anisonema minus, Sandon; and Cercobodo vibrans, 

 Sandon). An eighth species, Parapolytoma satura, Jameson, is 

 questionably limited to the soil. 



The relative frequency of animal flagellates found in 146 soils 

 from different parts of the world is shown in the table on p. 355, 

 condensed from Sandon's Chart II. 



It is safe to say that the first 10 of these are characteristic of 

 flagellates of the soil and may be found practically anywhere, par- 

 ticularly in arable and garden soils. The last 10 may well be 

 regarded as chance specimens and without significance in soil 

 biology. The twenty-eight intermediate species may or may not 

 be present, depending upon environmental conditions of food 

 (bacterial), moisture, relative acidity, etc., the great majority being 

 species which are also found as water-dwelling or as coprozoic 

 forms. Furthermore, methods of examination are not sufficiently 

 perfected to determine whether a given form actually lives in the 

 soil or is dormant there and has developed in the artificial culture 

 medium subsequently used. It is quite possible that certain cysts 

 never develop in earth, and it is also quite possible that active 

 forms in the soil are killed by drying or by the conditions of 

 culture. 



In addition to the list of flagellates described by Sandon other 

 workers have described different species from the soil, bringing the 

 total number of soil flagellates up to about 75 species. This esti- 

 mate, however, includes several forms which should be regarded as 

 rhizopods (particularly the Bistadiidae and flagellated swarmers of 

 the Mycetozoa) and plant flagellates. Amongst additional animal 

 flagellates we should include Codosiga botrytis, Ehr. (Goodey, 1911, 

 rare); Salpingoeca convallaria, Stein, and S. ampullacea, Braun 

 (Wolff, 1912); Rodo irrricolus (Martin, 1912); Pleuromonas jaculans, 

 Perty (Fellers and Allison, 1920; Fantham, 1922-1924; Wolff, 1912); 

 Phyllomonas contorta, Klebs (Wolff, 1912); Hexamitus inflatus, Duj. 

 (Fellers and Allison, 1920); Monas guttula, Ehr. (several observers); 

 Monas vivipara, Ehr. (several observers); Astasia sp. (Fellers and 

 Allison, 1920); Peranema trichophorum (various observers) ; Urceolus 



