NON- PROTOZOAN FAUNA OF SOIL 353 



gizzard into fine particles and decomposing some of the organic matter 

 which may be present. The earth is then passed out of the body and 

 deposited as castings at the surface of the burrows. The soil is thus 

 well mixed with the organic matter and brought from the lower layers 

 to the surface. According to Darwin, ten tons of earth for each acre 

 of land are passed through the bodies of the earthworms every year in 

 some cases. This mechanical action of the worms upon the structure 

 of the soil is of great importance. Wollny 32 considered that the worms 

 were concerned with the decomposition of the nitrogenous compounds in 

 the soil; a soil containing worms was found to have a higher ammonium 

 content than the same soil free from worms. Soils containing earth- 

 worms and upon which grass was growing was found to contain more 

 ammonia, nitrate and total nitrogen than soils without worms and 

 grass, but this is probably due more to the grass than to the worms. 33 



It was suggested 34 that earthworms increase plant growth by increas- 

 ing the surface of soil due to excreta, thus affecting the water-holding 

 capacity of the soil and movement of water. These organisms are 

 commonly considered to exert an important influence upon the mechan- 

 ical transformation in soil as well as soil productivity as a result of 

 their effect upon nitrogen transformation. 35 Russell, 36 however, pointed 

 out that earthworms do not appear to have any marked effect on the 

 production of plant food; their chief work is to act as cultivators, loosen- 

 ing and mulching the soil, facilitating aeration and drainage by their 

 borrows. 



Oligochaeta-Limicolac or Enchytraeidae. This family is character- 

 ized by their whitish appearance and presence of more than two straight 

 setae in some of the bundles. Moist soils, especially those rich in 

 organic matter, will contain large numbers of these organisms. Thomp- 

 son found as many as 86 forms in a 9-inch cube of the upper 3 inches of 



32 Wollny, E. Die Zersetzung der organischen Stoffe. 1897, p. 39. 



33 Blanck, E., and Giesecke, F. Uber den Einfluss der Regenwurmer auf die 

 physikalischen und biologischen Eigenschaften des Bodens. Ztschr. Pflanzener- 

 nahr. Dung., 3B: 198-210. 1924. 



34 Kohswitz, H. G. Untersuchungen Uber den Einfluss der Regenwurmer 

 auf Boden und Pflanze. Bot. Archiv., 1: 315-331. 1922. 



35 Aichberger, R. V. Untersuchungen uber die Ernahrung des Regenwurmes. 

 Arb. Biol. Inst. Miinchen. No. 4, Kleinwelt. 1914; Heymons, R. Der Einflusz 

 der Regenwurmer auf Beschaffenheit und Ertragsfahigkeit des Bodens. Ztschr. 

 Pflanzenernahr. Dung., 2A: 97-129. 1923. 



36 Russell, E. J. The effect of earthworms upon soil productiveness. Jour. 

 Agr. Sci., 3: 346. 1910. 



