第24章

The burrows which run far down into the ground, generally, or at least often, terminate in a little enlargement or chamber.Here, according to Hoffmeister, one or several worms pass the winter rolled up into a ball.Mr.Lindsay Carnagie informed me (1838) that he had examined many burrows over a stone-quarry in Scotland, where the overlying boulder-clay and mould had recently been cleared away, and a little vertical cliff thus left.In several cases the same burrow was a little enlarged at two or three points one beneath the other; and all the burrows terminated in a rather large chamber, at a depth of 7 or 8 feet from the surface.These chambers contained many small sharp bits of stone and husks of flax-seeds.They must also have contained living seeds, for on the following spring Mr.Carnagie saw grass-plants sprouting out of some of the intersected chambers.I found at Abinger in Surrey two burrows terminating in similar chambers at a depth of 36 and 41 inches, and these were lined or paved with little pebbles, about as large as mustard seeds; and in one of the chambers there was a decayed oat-grain, with its husk.Hensen likewise states that the bottoms of the burrows are lined with little stones; and where these could not be procured, seeds, apparently of the pear, had been used, as many as fifteen having been carried down into a single burrow, one of which had germinated. We thus see how easily a botanist might be deceived who wished to learn how long deeply buried seeds remained alive, if he were to collect earth from a considerable depth, on the supposition that it could contain only seeds which had long lain buried.It is probable that the little stones, as well as the seeds, are carried down from the surface by being swallowed; for a surprising number of glass beads, bits of tile and of glass were certainly thus carried down by worms kept in pots; but some may have been carried down within their mouths.The sole conjecture which I can form why worms line their winter- quarters with little stones and seeds, is to prevent their closely coiled-up bodies from coming into close contact with the surrounding cold soil; andsuch contact would perhaps interfere with their respiration which is effected by the skin alone.

A worm after swallowing earth, whether for making its burrow or for food, soon comes to the surface to empty its body.The ejected earth is thoroughly mingled with the intestinal secretions, and is thus rendered viscid.After being dried it sets hard.I have watched worms during the act of ejection, and when the earth was in a very liquid state it was ejected in little spurts, and by a slow peristaltic movement when not so liquid.It is not cast indifferently on any side, but with some care, first on one and then on another side; the tail being used almost like a trowel.When a worm comes to the surface to eject earth, the tail protrudes, but when it collects leaves its head must protrude.Worms therefore must have the power of turning round in their closely-fitting burrows; and this, as it appears to us, would be a difficult feat.As soon as a little heap has been formed, the worm apparently avoids, for the sake of safety, protruding its tail; and the earthy matter is forced up through the previously deposited soft mass.The mouth of the same burrow is used for this purpose for a considerable time.In the case of the tower-like castings (see Fig.2) near Nice, and of the similar but still taller towers from Bengal (hereafter to be described and figured), a considerable degree of skill is exhibited in their construction.Dr.King also observed that the passage up these towers hardly ever ran in the same exact line with the underlying burrow, so that a thin cylindrical object such as a haulm of grass, could not be passed down the tower into the burrow; and this change of direction probably serves in some manner as a protection.

Worms do not always eject their castings on the surface of the ground.When they can find any cavity, as when burrowing in newly turned-up earth, or between the stems of banked-up plants, they deposit their castings in such places.So again any hollow beneath a large stone lying on the surface of the ground, is soon filled up with their castings.According to Hensen, old burrows are habitually used for this purpose; but as far as my experience serves, this is not the case, excepting with those near the surface in recently dug ground.I think that Hensen may have been deceived by the walls of old burrows, lined with black earth, having sunkin or collapsed; for black streaks are thus left, and these are conspicuous when passing through light-coloured soil, and might be mistaken for completely filled-up burrows.

It is certain that old burrows collapse in the course of time; for as we shall see in the next chapter, the fine earth voided by worms, if spread out uniformly, would form in many places in the course of a year a layer 0.2 of an inch in thickness; so that at any rate this large amount is not deposited within the old unused burrows.If the burrows did not collapse, the whole ground would be first thickly riddled with holes to a depth of about ten inches, and in fifty years a hollow unsupported space, ten inches in depth, would be left.The holes left by the decay of successively formed roots of trees and plants must likewise collapse in the course of time.