As doubts have been expressed by some writers whether worms ever swallow earth solely for the sake of making their burrows, some additional cases may be given. A mass of fine reddish sand, 23 inches in thickness, left on the ground for nearly two years, had been penetrated in many places by worms; and their castings consisted partly of the reddish sand and partly of black earth brought up from beneath the mass. This sand had been dug up from a considerable depth, and was of so poor a nature that weeds could not grow on it. It is therefore highly improbable that it should have been swallowed by the worms as food. Again in a field near my house the castings frequently consist of almost pure chalk, which lies at only a little depth beneath the surface; and here again it is very improbable that the chalk should have been swallowed for the sake of the very little organic matter which could have percolated into it from the poor overlying pasture. Lastly, a casting thrown up through the concrete and decayed mortar between the tiles, with which the now ruined aisle of Beaulieu Abbey had formerly been paved, was washed, so that the coarser matter alone was left. This consisted of grains of quartz, micaceous slate, other rocks, and bricks or tiles, many of them from 1/20 to 1/10 inch in diameter. No one will suppose that these grains were swallowed as food, yet they formed more than half of the casting, for they weighed 19 grains, the whole casting having weighed 33 grains. Whenever a worm burrows to a depth of some feet in undisturbed compact ground, it must form its passage by swallowing the earth; for it is incredible that the ground could yield on all sides to the pressure of the pharynx when pushed forwards within the worm’s body. That worms swallow a larger quantity of earth for the sake of extracting any nutritious matter which it may contain than for making their burrows, appears to me certain. But as this old belief has been doubted by so high an authority as Claparède, evidence in its favour must be given in some detail. There is no _à priori_ improbability in such a belief, for besides other annelids, especially the _Arenicola marina_, which throws up such a profusion of castings on our tidal sands, and which it is believed thus subsists, there are animals belonging to the most distinct classes, which do not burrow, but habitually swallow large quantities of sand; namely, the molluscan Onchidium and many Echinoderms. {97}