This lump of red sandstone that has been rolled about in the sea, till all its points and angles are worn smooth, is now roughened again by the close and firm adhesion of extraneous substance, in the form of a cluster of shelly pipes, which twine irregularly over the surface of the boulder, and then start up erect with open mouths. These are the tubes of a species of _Serpula_, and the worm itself is seen now slowly emerging from one of them, and introducing its conical stopper, and elegant fans of white and scarlet filaments, to the genial daylight. Observe, however, that the tubes are not of the same diameter throughout. At the point where they start up from contact with the stone, they are considerably smaller than at the tip; and if we trace back the adherent portion along its tortuous course, we find that it constantly diminishes until it is but a slender white thread of stone. Now this slender extremity was formed first; and as the worm itself grew, so it progressively required a larger and yet a larger habitation; which was readily provided of the due dimensions, because the material, which is limestone, was secreted by the swollen collar of the worm, and being freely poured out as required, was moulded of the proper calibre by the rotatory motion of the animal, combined with the special use of certain tactile organs for the purpose. The shelly tubes themselves afford us ocular evidence not only of their progressive formation, but also of the successive steps by which this was effected. For at certain intervals of their length we perceive rings of the common stony substance, which mark the rim or mouth of the tube as it existed after each periodic increase. The mouth of the tube is, as we see, slightly expanded in a trumpet fashion; but as the general cylindrical figure is to be maintained, the next deposit of calcareous matter is not made at the very edge of the lip, but on a ring a little way within the margin, whence it is carried up, leaving the former margin slightly projecting. [Illustration: SERPULA.] Who could hesitate to assert that a history of past time is legibly written in the annulations of these stony tubes? And yet the creatures, with their tubes, have been but this instant created. But here is a tube of quite another construction, though inhabited by a kindred worm. It is wholly built up of sand, the inimitable architecture of the indwelling _Terebella_, who has thus succeeded in performing a task which defied the efforts of that too industrious artizan,--the familiar of the renowned Michael Scott.[67] Our worm has certainly spun a rope of sand, and one which holds together with surprising tenacity.