386 CHARLES ROBERT DARWIN. 



baby. You will perceive by this that I have a fine 

 degree of paternal fervor." 



In 1881, " The Formation of Vegetable Mould, 

 through the Action of Worms, with Observations 

 on their Habits," was published. " Fragments of 

 lournt marl, cinders, etc., which had been thickly 

 strewed over the surface of several meadows were 

 found, after a few years, lying at a depth of some 

 inches beneath the turf, but still forming a layer." 

 Ascertaining that this was the work of worms, 

 Darwin made a study of their structure, habits, 

 and work, in his garden, his fields, and in pots of 

 earth kept in his study. The intelligence of 

 w r orms, the construction of their burrows, and the 

 amount of labor they can perform, are described 

 in a most entertaining manner. Over fifty thou- 

 sand worms are found in a single acre of land, or 

 about three hundred and fifty-six pounds. "In 

 many parts of England a weight of more than ten 

 tons of dry earth annually passes through their 

 bodies, and is brought to the surface, on each acre 

 of land. . . . Worms prepare the ground in an ex- 

 cellent manner for the growth of fibrous-rooted 

 plants and for seedlings of all kinds. They peri- 

 odically 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 gardener who prepares 

 fine soil for his choicest plants. . . . The plough 

 is one of the most ancient and most valuable of 

 roan's inventions ; but long before he existed the 



