_ THE EARTHWORM 107 
feeling, however, is very highly developed, the slightest 
jarring or movement of the soil being instantly felt. 
Food.. Worms live on decaying vegetable matter ; 
some of this is obtained from the earth swallowed in 
burrowing ; but most of it is procured from leaves and other 
parts of plants which are dragged into the burrows. It is 
at night the animal searches for food on the surface of the 
ground. ‘The fore part of the body is then forced out, the 
tail being generally fixed in the burrow to admit of 
instantaneous retreat in case of danger. 
Uses. Small as these animals are, they do exceedingly 
useful work, the extent of which is made possible by the 
immense numbers in which they exist. According to 
some writers, these reach from fifty to sixty thousand per 
acre. The worms swallow the soil in large quantities and 
extract from it the nutritious portions. The rest, which 
becomes even more finely divided in its passage through 
the animal, is deposited at the surface in the form 
of castings. Darwin estimated that in this way about 
fifteen tons per acre were annually brought up and spread 
over the ground, Mr. A. Millson, as the result of 
numerous experiments in W. Africa, calculated that 62,233 
tons of subsoil were brought to the surface each year over 
every square mile of ground. The leaves and _ other 
decaying vegetable matter dragged into the burrows help 
to enrich the soil, and the openings formed by their 
. passages through the ground give access to the air from 
~ above, and. furnish drainage channels for water which 
otherwise would be unable to get away. 
Notr.—In examining small animals like the Earthworm it is 
not at all necessary that each pupil should be provided with an 
unfortunate specimen, which could not fail to be more or less 
injured, perhaps mutilated, during the process of investigation. 
Where classes are sinall, a shallow box containing a few inches of 
