444 Bibliographical Notice. 
his many invaluable works; and he now publishes the results in a 
most interesting little volume, in which he fully vindicates the claims 
of his humble clients to be regarded as entities of considerable im- 
portance. 
Mr. Darwin claims for earthworms the performance of two most 
important functions. He maintains that they are, to a great ex- 
tent, the actual makers of what we are accustomed to call “ vege- 
table mould,” and, secondly, that they are great workers in, and 
transporters of, this mould when formed. 
These animals are shown to contribute to the formation of the 
substance called vegetable mould in several ways. They feed chiefly 
on vegetable substances, which may be either already mixed with 
the existing mould, or dragged by them into their burrows for the 
purpose or, in the first instance, to stop the mouth of the hole, or 
to line the interior of the upper part of the burrow—a practice for 
the discovery of which we are indebted to Mr. Darwin. These 
vegetable materials are torn into minute shreds and swallowed by 
the worms, in addition to the soil which they take for the purpose 
of extracting nourishment from it; and the residue of this food, 
passing through their bodies and getting mixed with their intestinal 
secretions, goes to increase the stratum of mould. They further 
assist in the process of mould-formation by throwing up their cast- 
ings over the dead leaves lying on the surface of the ground, which 
are thus brought at once into the layer of soil and protected from 
atmospheric action until they either become slowly decomposed or 
are converted into food for worms, in either case adding to the 
thickness of mould. And they add to the quantity of mineral 
matter in the soil by bringing up the finer particles of the subsoil, 
into which they burrow to some depth, and facilitating their mix- 
ture with the other materials. The reality of this influence is 
proved in a striking manner by an experiment made by Von Hensen 
and cited by Mr. Darwin from that gentleman’s admirable article 
on the natural history of earthworms, published in Siebold and 
Kolliker’s ‘ Zeitschrift ’ for 1877. ‘* Von Hensen,” he says, ‘* placed - 
two worms in a vessel 18 inches in diameter, which was filled with 
sand, on which fallen leaves were strewed ; and these were soon 
dragged into their burrows to a depth of 3 inches. After about six 
weeks an almost uniform layer of sand, a centimetre (‘4 inch) in 
thickness, was converted into humus by having passed through the 
alimentary canals of these two worms.” 
As workers of the soil, their influence seems to be of equal im- 
portance. As they are constantly swallowing the mould in which 
they live, and reducing the organic matter contained in it to the 
smallest possible particles, they effect a most intimate intermixture 
of all the parts, acting, as Mr. Darwin points out, “just in the same 
way as a gardener in preparing the finest soil for his choicest plants, 
bringing it into a state in which it is well fitted to retain moisture 
and to absorb all soluble substances, as well as for the process of 
nitrification.” Their burrows, which frequently descend to a con- 
siderable depth, give access to air and water, and also, by yielding 
