Читать книгу Intelligence in Plants and Animals онлайн

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Two ways are adopted by worms in excavating their burrows. Either the earth is pushed away on all sides or it is swallowed by the animal. In the former case the worm inserts the stretched-out and attenuated anterior extremity of its body into any little crevice or hole, and the pharynx is pushed forward into this part, which consequently swells and pushes away the earth on all sides, the anterior extremity thus acting as a wedge. When placed in loose mould a worm will bury itself in between two and three minutes, but in earth that is moderately pressed down it often requires as many as fifteen minutes for its disappearance. But whenever a worm burrows to a depth of several feet in undisturbed compact ground, it must form its passage by swallowing the earth, for it is impossible that the ground could yield on all sides to the pressure of the pharynx when pushed forward within the worm’s body. Great depths are reached only during continued dry weather and severe cold, the burrows sometimes attaining to a depth of from seven to eight feet. The burrows run down perpendicularly, or, more commonly, obliquely, and are sometimes said to branch. Generally, or invariably as I think, they are lined with fine, dark-colored earth voided by the worm, so that at first they must be made a little wider than their ultimate diameter. Little globular pellets of voided earth, still soft and viscid, often dot the walls of fresh burrows, and these are spread out on all sides by the worm as it travels up or down its burrow, the lining thus formed becoming very compact and smooth when nearly dry and closely fitting the worm’s body. Excellent points of support are thus afforded for the minute reflexed bristles which project in rows on all sides from the body, thus rendering the burrow well adapted for the rapid movement of the animal. The lining appears also to strengthen the walls, and perhaps saves the worm’s body from being scratched, which would assuredly be the case when the burrows, as is occasionally observed, pass through a layer of sifted coal cinders. The burrows are thus seen to be not mere excavations, but may be compared with tunnels lined with cement. Those which run far down into the ground generally, or at least frequently, terminate in little chambers, where one or several worms pass the winter rolled up into a ball. Small pebbles and seeds as large as grains of mustard are carried down from the surface by being swallowed or within the mouths of worms, as well as bits of glass and tile, whose only use in their winter-quarters seems to be the prevention of their closely coiled-up bodies from coming into contiguity with the surrounding cold soil, for such contact would perhaps interfere with their respiration, which is effected by the skin alone.