J8 Field- Lab ou7'ers 



it varies, of course, according to their size, in which 

 they differ very greatly. There is a w^orm in Ceylon 

 about tw^o feet long ; in the Nilgiri Hills, already 

 mentioned, they are twelve or fifteen inches long and 

 as thick as a man's little finger ; while on the Amazon 

 there are some as much as two feet and a half long 

 and thick in proportion, and able therefore to do much 

 work. 



Seeing only the little dark heaps of soil thrown up 

 by worms on grass-plots and gravel-paths, heaps which 

 are soon washed down again by rain, one has some 

 difficulty in realizing the vast amount brought up in 

 the course of a year. But Mr. Darwin reckoned that 

 near Nice this amounts to from about fourteen to 

 eighteen tons to the acre ; this is supposing them to be 

 as numerous and active over the whole of a field as 

 they were in the one square yard chosen for observa- 

 tion ; but it is also supposing them to work for only 

 six months of the year, which he considered a low 

 estimate. The largest amount was brought up on very 

 poor pasture, where leaves were probably scarce, and 

 the worms had to swallow much earth in order to 

 obtain sufficient food. 



On the whole it seems probable that they bring up 

 more than ten tons of soil to the acre in many parts of 

 England year by year, and that the entire mass of 

 mould — the dark surface-soil of every field — passes 

 through their bodies in the course of a few years, and 

 is by these means sifted and rendered extremely fine, 

 besides being thoroughly impregnated with vegetable 

 and animal matter. Moreover, bones, twigs, leaves, 

 shells, are constantly being covered with castings, and 

 these further help to enrich the soil by their decay ; 



