256 THE OPEN COUNTRY 



Earth-worms are of the highest importance in the life of the 

 fields, which derive much of their fertility from the silent exertions 

 of these lowly invertebrates. The familiar representative of the group is the 

 common earth-worm (Lumbricus terrestris), whose general appearance is known to 

 all. Like other worms, its body is divided into a number of ring-like segments, 

 and the head is indistinct. In all earth-worms the body tapers at both ends, and 

 on the abdomen carries from two to four rows of hooked bristles, which act as 

 legs. Earth-worms bore almost vertical holes into the ground, and live on mould 

 and decaying vegetable-matter, contributing to the formation of fertile soil b}- 

 tilling up their holes with green or dead leaves. They swallow large quantities 

 of earth, which, after passing through them, is deposited in front of their holes, 

 thereby covering in time whatever may be there, and in this way in the course 

 of years a floor of paving-stones may be lowered a foot deep. Earth-worms 

 generally come to the surface in great haste when the ground in which they dwell 

 is disturbed or smartly trampled upon ; and it is generally supposed that they do 

 this in consequence of mistaking the disturbance for the approach of their dreaded 

 enemy, the mole. As a result of this mistake, they frequently perish miserably, 

 if they happen to come out on to dry and parched ground in full sunshine. 

 Worms are most frequently seen above ground on lawns or meadows in spring or 

 autumn when the dew is still on the grass. 



As regards the numerous slugs and snails of the field, it must 



Molluscs 



suffice to mention the common grey slug (Limax agrestis), which is 

 H inches in length, and grey in colour, with the keel set obliquely on the back, and 

 the shield marked with concentric lines, and the heath-snail (Helix ericetorum), 

 which has a greyish, depressed shell with brown bands, a large umbilicus, that 

 is to say, the conical cavity occupying the centre of the spire, and a nearly 

 circular mouth. 



