352 PRINCIPLES OF SOIL MICROBIOLOGY 



have a well-defined body cavity and are hermaphroditic. The setae 

 aid in locomotion. Various families are found in the soil. 



The occurrence of earthworms in the soil has been of common 

 knowledge since the work of Darwin and Hensen. 26 They are especially 

 abundant in forest soils and soils rich in organic matter 27 while they 

 are almost absent in sandy soils. Heimburger 28 suggested that a cor- 

 relation exists between the degree of moisture of the soil and species 

 of earthworms inhabiting it. The worms react definitely to atmos- 

 pheric moisture but less sharply than to contact with moist substrate. 



To determine the numbers of earthworms in the soil, a certain 

 volume of it is spread in a thin layer on a flat surface; when the soil 

 begins to dry, the animals begin to move rapidly and can be counted. 

 Moist soil may also be covered with a solution of sugar or powdered 

 KHSO4, which will bring the worms to the surface. Morris 29 found 

 1,010,101 earthworms per acre of manured soil and 457,912 per acre 

 of unmanured soil. The greatest numbers occurred at a depth of two 

 and three inches. The following species of earthworms were found in 

 the soil by France: Eisenia rosea, Lumbricus terrestris, Lumbricus 

 rubellus, Allolobophora aporata, Helodrillus octaedrus. It was estimated 

 that between 200 and 1000 pounds of earthworms are present in an 

 acre of soil. Thompson 30 found eighteen individuals in a nine inch cube 

 of the upper three inches of a pasture soil. 



Soil reaction has an influence upon the development of earthworms. 31 

 The worms feed not only upon plant residues, but also on soil organisms. 

 France found various algae, fungus mycelium, protozoa and yeasts 

 in the excreta of earthworms. 



The animals pass earth through their bodies, grinding it in the 



26 Darwin, Ch. Vegetable mould and earthworms. London. J. Murray. 

 1881 ; D. Appleton, 1900. Hensen, V. Uber die Fruchtbarkeit des Erdbodens in 

 ihrer Abhiingigkeit von den Leistungen der in der Erdrinde lebenden Wiirmer. 

 Landw. Jahrb., 11: 661-698. 1882. 



27 Remele, E., Schellhorn, and Krause, M. Anzahl und Bedeutung der niederen 

 Organismen in Wald und Moorboden. Ztschr. Forst. u. Jagdwes., 31: 575-606. 

 1899. 



28 Heimburger, H. V. Reactions of earthworms to temperature and atmos- 

 pheric humidity. Ecology, 5: 276-282. 1924. 



29 Morris, H. M. Rothamsted Station Rept. for 191S-1920, p. 20. 



30 Thompson, M. The soil population. An investigation of the biology of 

 the soil in certain districts of Aberystwyth. Ann. Appl. Biol., 11: 349-394. 

 1924. 



31 Arrhenius, O. Influence of soil reaction on earthworms. Ecology, 2: 

 255-262. 1921. 



