Chap. VII. CONCLUSION. 313 



foot-stalks, unless tlie basal part of the blade 

 is as narrow as the apex, or narrower than it. 



When we behold a wide, turf-covered 

 expanse, we should remember that its smooth- 

 ness, on which so much of its beauty depends, 

 is mainly due to all the inequalities having 

 been slowly levelled by worms. It is a mar- 

 vellous reflection that the whole of the super- 

 ficial mould over any such expanse has passed, 

 and will again pass, every few years through 

 the bodies of worms. The plough is one of 

 the most ancient and most valuable of man's 

 inventions; but long before he existed the 

 land was in fact regularly ploughed, and still 

 continues to be thus ploughed by earth-worms. 

 It may be doubted whether there are many 

 other animals which have played so important 

 a part in the history of the world, as have 

 these lowly organised creatures. Some other 

 animals, however, still more lowly organised,^ 

 namely corals, have done far more conspicuous 

 work in having constructed innumerable reefs 

 and islands in the great oceans ; but these are 

 almost confined to the tropical zones. 



