BACKGROUND OF DARWINISM—THE WEB OF LIFE 213 
stalks of leaves and twigs into it; and, most of all, by throwing up such 
infinite numbers of lumps of earth called worm-casts, which, being 
their excrement, is a fine manure for grain and grass. Worms prob- 
ably provide new soil for hills and slopes where the rain washes the 
earth away; and they affect slopes probably to avoid being flooded. 
.... The earth without worms would soon become cold, hard- 
bound, and void of fermentation, and consequently sterile... .. 
These hints we think proper to throw out, in order to set the inquisitive 
and discerning at work. A good monograph of worms would afford 
much entertainment and information at the same time, and would 
open a large and new field in natural history.” 
The monograph that Gilbert White wished for in 1777 was pub- 
lished by Darwin in 1881, the year before he died—‘the completion,” 
he said, “of a short paper read before the Geological Society more than 
forty years ago.” With his characteristic thoroughness and patience 
he worked out the part that earthworms have played in the history 
of the earth, and proved that they deserve to be called the most useful 
animals. By their burrowing they loosen the earth, making way for 
the plant rootlets and the raindrops; by bruising the soil in their 
gizzards, they reduce the particles to more useful, powdery form; by 
burying the surface with castings brought up from beneath, they have 
been for untold ages ploughers before the plough, and by burying leaves 
they have made a great part of the vegetable mould over the whole 
earth. In illustration of the last point, we may notice that we recently 
found thirteen midribs of the leaves of the rowan, or mountain ash, 
radiating round one hole like the spokes of a wheel; the withering 
leaflets had been carried down, and two were sticking up at the mouth 
of the burrow; that meant o1 leaflets to one hole. Darwin showed 
that there often are 50,000 (and there may be 500,000) earthworms 
in an acre; that they often pass ten tons of soil per acre per annum 
through their bodies; and that they often cover the surface at the rate 
of three inches in fifteen years. Though our British worms only pass 
out about 20 oz. of earth in a year, the weights thrown up in a year on 
two separate square yards which Darwin watched were respectively 
6.75 lb. and 8.387 Ib., which correspond to 14} and 18 tons per acre 
per annum. — 
We follow the work further and it becomes evident that the con- 
stant exposure of the soil bacteria on the surface is bound to be 
important, on the one hand, in allowing them to be scattered by wind 
and rain, on the other in exposing them to the beneficent action of the 
