Let us resume our grubbing in the heterogeneous heap of matters
with which the dredge has enriched us. The tube-dwelling _Annelida_
are generally prominent in such collections, and accordingly we see
conspicuous here great and small heaps of contorted tubes, that look
as if a batch of tobacco-pipe stems had become agglutinated together,
and strangely twisted in the baking. These are the shelly tubes of the
beautiful scarlet Serpula,[140] a general favourite in our aquaria,
easily and abundantly procured, and readily maintained in health
and beauty for a considerable period. I need scarcely describe the
general appearance of an object so commonly kept, and so frequently
gazed upon. Many tubes are usually found growing together, adhering
to the same shell, bit of broken pottery, or small stone; all much
intertwined, and mutually adherent, so that it is practically hopeless
to attempt to isolate one. Yet by studying many specimens we are able
to ascertain that each individual is at first a very slender tube of
white calcareous shell, not thicker than sewing-cotton;[141] this
rapidly increases both in thickness and in length, soon rising from
its support, to which it at first adhered by the lime deposited in a
soft state, and continuing the rest of its growth free, in a direction
forming various angles with the ground line, and most irregularly
twined and contorted. For the final half of its length, or thereabout,
the tube attains a diameter of one-fourth of an inch, the walls being
sufficiently thick to be solid, yet leaving an ample cavity for the
residence of the industrious mechanic, who thus skilfully builds up his
own house.
[Illustration: