Page:Popular Science Monthly Volume 20.djvu/307

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293
EARTH-WORMS AND THEIR WORKS.

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 PSM V20 D307 Tower like casting ejected by a species of perichaeta.jpgFig. 2.—A Tower-like Casting probably ejected by a Species of Perichæta (from the Botanic Garden, Calcutta: of natural size, engraved from a photograph). watched worms during the act of ejection, and when the earth was in a very liquid state it was ejected in little spurts, and when not so liquid by a slow. peristaltic movement. 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. As soon as a little heap is 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." Some of the towers, as the figure shows, exhibit a considerable degree of skill in their construction. The castings are not always ejected on the surface of the ground, but are often lodged in any cavity that may be met in burrowing. The burrows run down, sometimes perpendicularly, generally a little obliquely, to a depth of three, six, and even eight feet, and are usually lined with a thin layer or plaster of fine, dark-colored earth which the animals have voided, in addition to which a lining is made, near the mouths, of leaves, also plastered. Bits of stones and seeds are also sometimes found in the bottom of the burrows, having been taken down apparently with a purpose.

The amount of earth brought up by worms from beneath the surface has been carefully estimated by observing the rate at which stones and other scattered objects on top of the ground are buried. A piece of waste, swampy land, which was inclosed, drained, plowed, harrowed, and thickly covered with burned marl and cinders, and sowed with grass, in 1822, fifteen years afterward, presented the appearance, where holes were dug into it, shown by Fig. 3, the scale of which is half that of nature. Beneath a sod an inch and a half thick was a layer of vegetable mold, free from fragments of every kind, two and a half inches thick. Under this was another layer of mold, an inch and a half thick,