its hole, it drags leaf-stalks in by the base so as to fill it faster; but as soon as it comes to close quarters, it turns and drags the rest of the stalks in by the tips. Triangles of paper were given worms instead of leaves, and they likewise drew them in in the easiest way, apparently at the first trial. When worms can not obtain leaves, petioles, sticks, etc., with which to plug up the mouths of their burrows, they often protect them by little heaps of stones; and such heaps of smooth, rounded pebbles may frequently be seen in gravel-walks. A lady interested in this study removed the little heaps of stones from the mouths of several burrows, and cleared the surface of the ground for some inches all around. She went out on the following night with a lantern, and saw the worms, with their tails fixed in their burrows, dragging the stones inward by the aid of their mouths. After two nights some of the holes had eight or nine small stones over them; after four nights one burrow had about thirty and another thirty-four stones, and one of the stones weighed two ounces. The strength of worms is also shown by their often displacing stones in a well-trodden gravel-walk, a task that sometimes demands considerable effort.
Worms excavate their burrows in two ways: by pushing away the earth on all sides where the ground is loose or only moderately compact, and where they are able to disappear from sight with surprising agility; and by swallowing the dirt, where the ground is hard, and ejecting the swallowed earth afterward in the form of the "castings" which are found at the mouths of their burrows. Worms also swallow earth to extract the nutritous matter which may be contained in it, and in larger quantity than for making their burrows; and the residue of this, after the nutriment is extracted, is also cast out. The deposition of castings, then, is no insignificant part of the labor that they perform, and leaves very perceptible traces upon the surface. The castings may be seen by any one who will take the pains to look for them, and often in garden-walks without looking for them, piled up in the shape of towers of greater or less height around the burrows. The towers formed by a naturalized East Indian worm, at Nice, France, which are sometimes distributed as thickly as five or six to a square foot, are built to a height of from two and a half to three inches. The tower of a perichæta in the Botanic Garden at Calcutta, of which Fig. 2 is an exact representation, measured three and a half inches high and 1·35 inch in diameter. One tower from Calcutta was five inches high and two and a half inches in diameter; and the average weight of twenty-two castings sent Mr. Darwin from Calcutta was an ounce and a quarter. The largest castings mentioned came from the Nilgiri Hills in South India, seven thousand feet above the sea, and afforded one specimen that weighed a quarter of a pound, the largest convolutions of which were about an inch in diameter. The manner of forming the casting is described by Mr. Darwin: "A worm after swallowing earth, whether for making its
