354 



PRINCIPLES OF SOIL MICROBIOLOGY 



pasture soil, including several species of Fredericia and Enchytraeus 

 (E. albidus). France found species of Enchytraeus, Fredericia and 

 Anachacta in the soil. According to Jegen, 37 these are capable of 

 neutralizing the injurious effect of certain nematodes in the soil; he also 

 claimed that they play a role in the formation of humus in the upper 

 soil layers. They are very sensitive to drying and to lack of oxygen. 

 Their relative abundance is indicated by the following numbers found 

 in one square meter of different soils, at different seasons of the year. 

 They were practically absent in heavy clay soils, as shown in the fol- 

 lowing summary: 



SOIL TYPE 



Spring 



Summer (dry). . 

 Summer (moist) 



Autumn 



Winter 



60- 100 



28- 75 



70- 300 



100- 450 



800-1600 



SANDY SOIL 



6,900- 9,000 

 2,000- 4,900 

 6,500- 8,500 

 7,000-11,000 

 6,800- 9,400 



HUMUS SOIL 



30,000- 70,000 

 11,800- 16,000 

 28,000- 50,000 

 60,000-150,000 

 50,000-120,000 



Tardigrada. The tardigrads are a group of Annelids, although 

 they are often wrongly classified with the Arachnids and Arthropoda. 38 

 The organs of locomotion are unarticulated, with more or less retract- 

 ible parapodia. The body is 1 to 10 mm. long, cylindrical, often al- 

 most worm-like. Some are without eyes, some have compound eyes 

 in the form of black or red spots. The sexes are separate. During 

 a period of dryness, they hibernate. Hibernation my last for years 

 without injury to the organism. The tardigrads can withstand con- 

 siderable heat and cold. Under unfavorable conditions, they encyst; 

 regeneration of the organs follows this stage. Various species are 

 found in the soil. France - found this group represented by the genera 

 Macrobiotus and Milnesium. 



ARTHROPODA 



Crustacea. The crustaceans are represented in the soil by the 

 Copepoda 39 (family Harpacticidae) and the Isopoda, 40 or higher crus- 



37 Jegen, G. Bedeutung der Enchytraeiden fur die Humusbildung. Landw. 

 Jahrb. Schweiz, 34: 55-71. 1920. 



38 Richters, F. Tardigrada. Handworterbuch der Naturwissenschaften., 

 9. 1913. 



39 Van Douwe, C, and Neresheiner, E. Copepoda. Die Susswasserfauna 

 Deutschlands. H. 11, 1909. 



40 Richardson. H. A monograph on the Isopods of North America. U. S. 

 Nat. Mus. Bui. 64. 1905. 



