CHAPTER X 

 HE EARTHWORM AND ANNELIDS IN GENERAL 



i. THE EARTHWORM 



(Lumbricus terrestris Linnaeus) 



THE earthworm, Lumbricus terrestris, 1 lives in the ground where 

 the soil is not too dry or sandy, coming to the surface only at 

 night or after a rain. The burrows are cylindrical and penetrate 

 to a depth of from six inches to several feet. Evidences of the 

 presence of earthworms are found in the little heaps of black 

 earth, called " castings," which strew the ground, being espe- 

 cially noticeable early in the morning. These castings are really 

 the faeces cast out from the alimentary canal of the worm. Dar- 

 win (139) estimated that more than eighteen tons of earthy cast- 

 ings are carried to the surface in a single year on one acre of 

 ground, and in twenty years a layer three inches thick would be 

 transferred from the subsoil to the surface. This continuous 

 honeycombing of the soil makes the land more porous, and insures 

 the better penetration of moisture, and the continuous working 

 over of the surface layers of earth also helps to make the soil more 

 fertile. 



External Features. Lumbricus terrestris reaches a length of 

 from six inches to as much as a foot. It is capable of pronounced 

 extensions and contractions, so that the length of an individual 

 varies, as does also its diameter. Although its body is cylindroid 

 it is possible to recognize dorsal, ventral, and lateral surfaces. 

 Movement takes place in a definite direction, the advancing 



1 This is one of many species of earthworms. In many parts of this 

 country the species Allolobophora (Helodrilus) longa or one of the species of 

 Diplocardia are more abundant in cultivated soiL 



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