42 THE BIOLOGY OF AN ANIMAL. 



ing a depth of six or eight feet. The earthworm is a nocturnal 

 animal, and during the day lies quiet in its burrow near the sur- 

 face, extended at full length, head uppermost. At night it 

 becomes very active, and, thrusting the fore end of the body 

 far out, explores the vicinity in all directions, though still clinging 

 fast, as a rule, to the mouth of the burrow by the hinder end. 

 In tliis way the worm is able to forage, seizing leaves, pebbles, 

 and other small objects, and dragging them into the burrow. 

 Some of these are devoured ; the remainder (including the peb- 

 bles, etc.) are used to line the upper part of the burrow, and to 

 plug up its opening when the worm retires for the day. Be- 

 sides bits of leaves and animal matter, earthworms swallow large 

 quantities of earth, which is passed slowly through the alimentary 

 canal, so that any nutritious substances contained in it may be 

 digested and absorbed. This earth is generally swallowed at a 

 considerable distance below the surface of the ground, and is 

 finally voided at the surface near the opening of the burrow. 

 In this way arise the small piles of earth (" castings " or faeces} 

 which every one has seen, especially in the morning, wherever 

 earthworms abound. Very large quantities of earth are thus, 

 brought to the surface by earthworms in some cases, accord- 

 big to Darwin's estimates, more than eighteen tons per acre in 

 a single year. In fact, most soils are continually being worked 

 over by worms; and Darwin has shown that these humble 

 creatures, in the course of centuries, have helped to bury huge 

 rocks and the ruins of ancient buildings.* 



The earthworm has no ears, eyes, or any other well-marked 

 organs of special sense. Nevertheless and this is a point of 

 great physiological interest the fore end of the body is sensi- 

 tive to light ; for if a strong light be suddenly flashed upon this 

 part of the worm as it lies stretched forth, it will often " dash 

 like a rabbit into its burrow." The animal has a keen sense of 

 touch, as may be proved by tickling it ; and its sense of taste 

 must be well developed, since the worm is somewhat fastidious 

 in its choice of food. Earthworms appear to be quite deaf, but 

 possess a distinct, though feeble, sense of smell. 



* Darwin, Vegetable Mould and Earthworms. Appleton, N. Y., 1882. See 

 also White's Natural History ofSelborne, Index, references to " Earthworms/* 



