284 THE BIOLOGY OF THE SEASONS 



sea. The well-known parallel ledges along the slopes 

 of grass-clad hills are partly due to earthworm castings 

 caught on sheep-tracks, and thus we begin to connect 

 the earthworms not only with our wheat-supply, but 

 with our scenery. 



And as we began this short sketch by quoting Gilbert 

 White, so we shall close it by quoting Darwin. " When 

 we behold a wide turf -covered expanse, we should remember 

 that its smoothness, on which so much of its beauty de- 

 pends, is mainly due to all the inequalities having been 

 slowly levelled by worms. It is a marvellous reflection 

 that the whole of the superficial mould over any such area 

 has passed, and will again pass, every few years through 

 the bodies of the worms. The plough is one of the most 

 ancient and valuable of man's inventions ; but long before 

 he existed the land was in fact regularly ploughed, and 

 still continues to be ploughed, by earthworms. It may be 

 doubted whether there are many other animals which have 

 played such an important part in the history oj the world as 

 these lowly organised creatures. 1 ' 



