第22章

Two great piles of leaves had been left to decay in my grounds, and months after their removal, the bare surface, several yards in diameter, was so thickly covered during several months with castings that they formed an almost continuous layer; and the large number of worms whichlived here must have subsisted during these months on nutritious matter contained in the black earth.

The lowest layer from another pile of decayed leaves mixed with some earth was examined under a high power, and the number of spores of various shapes and sizes which it contained was astonishingly great; and these crushed in the gizzards of worms may largely aid in supporting them.Whenever castings are thrown up in the greatest number, few or no leaves are drawn into the burrows; for instance the turf along a hedgerow, about 200 yards in length, was daily observed in the autumn during several weeks, and every morning many fresh castings were seen; but not a single leaf was drawn into these burrows.These castings from their blackness and from the nature of the subsoil could not have been brought up from a greater depth than 6 or 8 inches.On what could these worms have subsisted during this whole time, if not on matter contained in the black earth? On the other hand, whenever a large number of leaves are drawn into the burrows, the worms seem to subsist chiefly on them, for few earth-castings are then ejected on the surface.This difference in the behaviour of worms at different times, perhaps explains a statement by Claparede, namely, that triturated leaves and earth are always found in distinct parts of their intestines.

Worms sometimes abound in places where they can rarely or never obtain dead or living leaves; for instance, beneath the pavement in well- swept courtyards, into which leaves are only occasionally blown.My son Horace examined a house, one corner of which had subsided; and he found here in the cellar, which was extremely damp, many small worm- castings thrown up between the stones with which the cellar was paved; and in this case it is improbable that the worms could ever have obtained leaves.Mr.A.C.Horner confirms this account, as he has seen castings in the cellars of his house, which is an old one at Tonbridge.

But the best evidence, known to me, of worms subsisting for at least considerable periods of time solely on the organic matter contained in earth, is afforded by some facts communicated to me by Dr.King.Near Nice large castings abound in extraordinary numbers, so that 5 or 6 were often found within the space of a square foot.They consist of fine, pale-coloured earth, containing calcareous matter, which after having passed through the bodies of worms and being dried, coheres with considerable force.I have reason to believe that these castings had been formed by species of Perichaeta, which have been naturalized here from the East. They rise like towers, with their summits often a little broader than their bases, sometimes to a height of above 3 and often to a height of 2.5 inches.The tallest of those which were measured was 3.3 inches in height and 1 inch in diameter.A small cylindrical passage runs up the centre of each tower, through which the worm ascends to eject the earth which it has swallowed, and thus to add to its height.A structure of this kind would not allow leaves being easily dragged from the surrounding ground into the burrows; and Dr.King, who looked carefully, never saw even a fragment of a leaf thus drawn in.Nor could any trace be discovered of the worms having crawled down the exterior surfaces of the towers in search of leaves; and had they done so, tracks would almost certainly have been left on the upper part whilst it remained soft.It does not, however, follow that these worms do not draw leaves into their burrows during some other season of the year, at which time they would not build up their towers.

From the several foregoing cases, it can hardly be doubted that worms swallow earth, not only for the sake of making their burrows, but for obtaining food.Hensen, however, concludes from his analyses of mould that worms probably could not live on ordinary vegetable mould, though he admits that they might be nourished to some extent by leaf-mould. But we have seen that worms eagerly devour raw meat, fat, and dead worms; and ordinary mould can hardly fail to contain many ova, larvae, and small living or dead creatures, spores of cryptogamic plants, and micrococci, such as those which give rise to saltpetre.These various organisms, together with some cellulose from any leaves and roots not utterly decayed, might well account for such large quantities of mould being swallowed by worms.It may be worth while here to recall the fact that certain species of Utricularia, which grow in damp places in the tropics, possess bladders beautifully constructed for catching minute subterranean animals; and these traps would not have been developed unless many small animals inhabited such soil.