20 HUMBLE CREATURES. 



compelled to do so by the spade of the labourer— 

 (and the worm is said to be very sensitive to any dis- 

 turbance of the soil in its vicinity), — ^when it wishes 

 to visit the surface in search of a mate, or in order to 

 discharge from its body the earth from which it has 

 extracted the decaying organized matter by the di- 

 gestive process. In this last operation it performs an 

 act of great utility to the agriculturist, inasmuch as 

 it enriches the surface soil by the deposition of those 

 little heaps of earth which we alluded to in a former 

 letter under the designation of "worm-castings." 

 We shall narrate briefly how this interesting circum- 

 stance was first discovered, showing at the same time 

 how important a part the worm plays in the con- 

 struction and fertilization of the soil. 



About twenty years since, an eminent naturalist*, 

 whilst visiting a friend in the country, was surprised 

 to hear from his host, that on some p astur e-\a,nA 

 which he possessed, an unaccountable change had 

 taken place in the character of the soil, which in 

 various fields had, without apparent cause, materially 

 increased in depth during the previous years, and 

 that cinders and other substances, which had ori- 

 ginally been thrown upon the surface, had apparently 

 sunk to a considerable depth in the soil. Curiosity 

 induced him to try a few experiments in order to 

 ascertain the cause of this strange phenomenon and 

 with this view he dug several holes in different fields • 



* Mr. Darwin. See 'Transactions of the Geoloo-ical Society' 

 2 ser. vol. v. p. 505 ; his paper " On the Formation of Mould." 



