Hubert M. Morris 303 



aeration and drainage of the soil. Since they pass smaller quantities of 

 soil through their bodies than in the case of earthworms, they probably 

 do not affect the soil to the same extent. 



Kostitcheff, in his work on the Russian " Black earth " (8), states that 

 the action of worms and insects in the soil is of great importance in 

 assisting in the breaking down of vegetable matter and the formation 

 of humus. In damp places where worms and insects are unable to hve, 

 the vegetable matter is broken down very much more slowly, and peat, 

 in which the vegetable matter still retains a certain amount of structure, 

 is formed instead of an amorphous humus. He does not agree with 

 Darwin with regard to the importance of earthworms in bringing soil 

 from the lower levels to the surface. 



In experiments carried out on earthworms, millepedes and Sciara 

 larvae Kostitcheff (9) found that they had little effect in accelerating the 

 decomposition of dead leaves, but he considers that after being once 

 passed through the animal, the material is then acted on by fungi and 

 bacteria, and again made available as food for the worms and insects, 

 and in this way the vegetable matter is eventually completely broken 

 down. 



Darwin estimated that earthworms brought to the surface of the 

 soil, in their "casts," sufficient earth to form annually a layer 0-2 inch 

 in depth, or dry earth weighing ten tons per acre, and that in 50 years 

 the upper ten inches of soil is completely turned over by them. 



Hensen, quoted by Darwin, calculated that there were 53,767 earth- 

 worms in an acre of garden soil, and found open burrows to the number 

 of 196,020 per acre, although Darwin states that he has seen them much 

 more numerous. Hensen estimated that there would be half as many 

 earthworms in an acre of cornfield as in garden soil. Darwin, who 

 obtained the number and weight of the "worm-casts" over certain 

 areas, did not give any relation between the number of "casts" and 

 the number of worms present. 



In the present investigation the numbers of worms found, 1,010,101 

 and 457,912 in the manured and control plots respectively, are very 

 much above Hensen's estimates. 



Summary. 



1 . Samples of soil were taken from two of the plots at the Rothamsted 

 Experimental Farm and all insects and other invertebrates were recorded 

 together with the approximate depths at which they occurred. 



