450 



TEXT-BOOK OF ZOOLOGY 



ones to vanish below. Thus they plough up the ground like the farmer. 

 Earth-worms, further, constantly loosen the soil by digging out new 

 passages to replace their old ones, which are constantly falling in. By 

 bringing the separate constituents of the soil constantly in contact with 

 fresh air and water, they bring about their disintegration and decom- 

 position. While thus preparing the soil, they also, as it were, manure 



it by dragging leaves 

 and similar sub- 

 stances down into 

 their runs, and finally 

 they thoroughly 

 mingle all these dif- 

 ferent materials like a 

 gardener who wishes 

 to produce a good rich 

 garden mould. Where 

 it occurs in enormous 

 quantities, the earth- 

 worm naturally may 

 become destructive by 

 pulling all the young 

 plants down into its 

 runs (see p. 72). It 

 is, however, incorrect 

 to charge it with 

 gnawing at the roots 

 of young plants, for in 

 the absence of teeth it 

 is difficult to see how 

 it could accomplish 

 this. 



Hence there is 

 every reason for pro- 

 tecting so remarkably 

 useful an animal, 



SECTION THROUGH UPPER STRATUM OF A FIELD 



which fifteen years previously, when a waste, swampy piece of 

 ground, was ploughed, drained, and thickly strewn with 

 burnt marl and cinders (one-half natural size). Through the 

 agency of earth-worms, in the course of years so much soil was 

 conveyed to the surface that a layer about 3 inches thick of 

 arable soil (A and B) was formed, while the marl and cinders 

 sank to a depth of from 3 to 4^ inches (into the layer C). 

 The stratum of subsoil (D), consisting of peaty sand, which 

 was not disturbed, contains (like the layer C) some rolled 

 pebbles of quartz. 



which, moreover, unprotected by defensive weapons, is exposed to the 

 attacks of an innumerable host of enemies. 



Allied Species. 



Owing to the nature of their body, all other worms require a moist 

 habitat. Hence many live in water. The nearest allies of the earth- 



