THE LIFE AND WORK OF DARWIN 221 



water for nearly four months. They live chiefly in 

 superficial mould, from four to ten inches in thick- 

 ness, but may burrow into the subsoil to a much 

 greater depth. The burrows are effected partly by 

 pushing away the earth on all sides, and partly by 

 swallowing it. In cold weather they may burrow to 

 a depth of from three to eight feet. The burrows 

 do not branch, and are lined by a layer of earth 

 voided by the worm ; they end in slightly enlarged 

 chambers in which the worm can turn round. 



Earthworms are nocturnal, remaining in the 

 burrows all day and coming out to feed at night. 

 They usually keep their tails in the burrows while 

 feeding, but may leave them entirely, and can crawl 

 backwards or forwards. They are very sensitive to 

 vibrations in the earth, a fact which can be shown 

 by placing a pot of earth containing them on a 

 piano. They do not, however, seem to hear, but 

 can distinguish light from darkness. 



Their food consists of leaves or fresh raw meat, 

 especially fat. 



The worms drag the leaves into their burrows, 

 using their lip to lay hold of them, and showing 

 judgment as to which end to draw them in by. 

 They swallow enormous quantities of earth, which 

 they void in spiral heaps, forming worm castings. 

 By means of the gizzard the earth is ground and 

 mixed with vegetable matter, and the castings are 

 hence of a black colour. They are in this way 

 always bringing earth from below and depositing it 

 on the surface. 



Darwin showed that a layer of coal cinders, spread 



