Earthworms
The earthworm is a limbless annelid worm with a hydrostatic skeleton that moves by means of peristalsis. This hydrostatic skeleton consists of a fluid-filled body cavity surrounded by an extensible body wall. The worm moves by radially constricting the anterior portion of its body, resulting in an increase in length via hydrostatic pressure. This constricted region propagates posteriorly along the worm's body. As a result, each segment is extended forward, then relaxes and re-contacts the substrate, with hair-like setae preventing backwards slipping. Earthworms increase four orders of magnitude during their lifetime and during this period the dimensions increase according to geometric similarity, or 'isometry'. Unlike rigid skeletons which cannot exhibit both geometric and stress similarity, the hydrostatic skeleton can maintain both forms which may be due to decoupling of weight and skeletal function.
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Famous quotes containing the word earthworms:
“How earthy old people become—mouldy as the grave! Their wisdom smacks of the earth. There is no foretaste of immortality in it. They remind me of earthworms and mole crickets.”
—Henry David Thoreau (1817–1862)