ANNELIDA : THE EARTHWORM, NEREIS 215 



out, but they rarely leave their burrows in other circum- 

 stances, except when they are about to die owing to the 

 attacks of parasitic maggots which are the young of certain 

 flies. The food of earthworms consists of the organic 

 matter in the soil, which they swallow, and of leaves both 

 fresh and decaying. They will also eat animal matter, and 

 are said to be very fond of fat. Charles Darwin has shown 

 the remarkable effects which these insignificant creatures 

 have upon the surface of the earth. By making the soil 

 more porous they expose the underlying rocks to the 

 disintegrating action of water, by solution owing to the 

 presence of carbon dioxide and other acids of the soil, and 

 by frost, and the small stones which eventually result from 

 this action are made still smaller by friction and solution 

 within their bodies. Thus they help in the formation of 

 the soil. At the same time they are aiding in its removal. 

 Their castings dry and crumble, and are blown about by 

 the wind or else are washed down by the rain. On sloping 

 ground this fine material tends to be carried away down- 

 wards, and thus the, denudation of hills is largely due to 

 the action of earthworms. On the other hand, their work 

 is highly beneficial to the farmer. The soil is by them 

 thoroughly mixed, submitted to the action of the air, and 

 constantly supplied with a fine "top dressing." It has 

 been calculated that earthworms bring up annually a layer 

 of soil one-fifth of an inch in thickness, which is spread by 

 the weather in the way we have described. Organic matter 

 is converted into a useful form and amalgamated with the 

 earth, and the latter is made easier of penetration by the 

 roots of plants. 



The commonest English earthworm is Lumbricus herculeus. 



The body of this animal is roughly cylindrical, 

 Features. Dut pointed in front and broadened behind. It 



reaches a length of seven inches. There is no 

 distinct head, but a lobe known as the prostomium over- 

 hangs the mouth, which is a crescentic opening on the 

 lower side of the front end. The body is divided into a 

 series of rings or segments, and at the hinder end is the 

 terminal anus. The first segment is known as the 

 peristomhcm and the mouth lies between it and the pro- 

 stomium. On the dorsal side, the latter projects across 



