ordinary vegetable mould, though he admits that they might be nourished to some extent by leaf-mould.[1] But we have seen that worms eagerly devour raw meat, fat, and dead worms; and ordinary mould can hardly fail to contain many ova, larvæ, 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.
The depth to which worms penetrate, and the construction of their burrows.—Although worms usually live near the surface, yet they burrow to a considerable depth during long-
- ↑ 'Zeitschrift für wissenschaft. Zoolog.' B. xxviii. 1877, p. 364.
