DARWIN. 151 



cinders was spread on December 20, 1842, over distinct 

 parts of a field near Down House, which had existed as 

 pasture for a very long time. At the end of November, 

 1871, a trench was dug across this part of the field, and 

 the nodules of chalk were found buried seven inches. A 

 similar change took place in a field covered with flints, 

 where in thirty years the turf was compact without any 

 stones. A pathway formed of loose-set flagstones was 

 similarly buried by worms, and became undistinguishable 

 from the rest of the lawn. And these are but a few of 

 the evidences of the wonderful action of worms, col- 

 lected by the activity of Charles Darwin and his sons. 



Earthworms were not only scrutinised in their out-of- 

 door work, but were kept in confinement and studied. 

 It appears they swallow earth both to make their burrows 

 and to extract all nutriment it may contain; they will 

 eat almost anything they can get their skin over. From 

 careful calculation it was shown that worms on an aver- 

 age pass ten tons of the soil on an acre of ground 

 through their bodies every year. It is, then, but a truism 

 to say that every bit of soil on the surface of the globe 

 must have passed through their bodies many times. 

 They were discovered to work mainly by night, when 

 hundreds may with care be discerned, with tails fixed 

 in their burrows, prowling round in circles, rapidly 

 retreating into holes, and strongly resisting efforts to 

 extract them. It was found by careful study that they 

 have no sense of hearing, but a most remarkable sensi- 

 tiveness to vibrations of the earth or even to contact with 

 air in motion. No book Darwin wrote was fuller of 

 interesting and undoubtedly correct observations. 



