THE EARTHWORM IN SCIENTIFIC LITERATURE 39 



times through, and will again pass many times through, the in- 

 testinal canals of worms. Hence the term 'animal tnould' would 

 be in some respects more appropriate than that commonly used, 

 'vegetable mould/ " In a summing up of Darwin's conclusions, 

 we cannot do better than to quote from his own summary, given 

 in the last chapter of his book. We quote in part: 



Worms have played a more important part in the history of 

 the world than most persons would at first suppose. In almost 

 all humid countries they are extraordinarily numerous and for 

 their size possess great muscular power. In many parts of Eng- 

 land a weight of more than .tgnjons (10,516 kilograms) of dry 

 earth jtnnually passes througfat tHeirJbodies and is brought to the 

 surface on_each acre of jand; so thatthe whole superficial bed of 

 vegetable mould passes^ through their bodies in the course of 

 every few years. From the collapsing of the old burrows the 

 mould is in constant though slow movement, and the particles 

 composing it are thus rubbed together. By these means fresh 

 surfaces are continually exposed to the action of the carbonic 

 acid in the soil, and of the humus-acids which appear to be still 

 more efficient in the decomposition of rocks. The generation of 

 the humus-acids is probably hastened during the digestion of the 

 many half-decayed leaves which worms consume. Thus, the par- 

 ticles of earth forming the superficial mould are subjected to con- 

 ditions eminently favourable to their decomposition and disin- 

 tegration. Moreover, the particles of the softer rocks suffer some 

 amount of mechanical trituration in the muscular gizards of the 

 worms, in which small stones serve as mill-stones . . . 



Worms prepare the ground in an excellent manner for the 

 growth of fibrous-rooted plants and for seedlings of all kinds. 

 They periodically expose the mould to the air, and sift it so that 

 no stones larger than the particles which they can swallow are 

 left in it. They mingle the whole intimately together, like a gar- 

 dener who prepares fine soil for his choicest plants. In this state 

 it is well fitted to retain moisture and to absorb all soluble sub- 

 stances, as well as for the process of nitrification. The bones of 

 dead animals, the harder part of insects, the shells of land mol- 

 luscs, leaves, twigs, etc., are before long all buried beneath the 

 accumulated castings of worms, and are thus brought in a more 

 or less decayed state within reach of the roots of plants. Worms 

 likewise drag an infinite number of dead leaves, and other parts 



