On such a noon, then, calm and quiet, the sun bright and cheerful, if
low and feeble, the tide tolerably low and the rocks accessible, we hie
down to some one or other of those ledges which have so often already
yielded their treasures to our search, and begin our wonted labours at
turning over the heavy angular masses. We soon find, attached to the
under surfaces of these, what seem to be irregular blobs of coloured
jelly of somewhat firm consistence, as if an invalid had been here
eating his calves’-foot jelly, whose trembling hand had dropped sundry
spoonfuls on the stones. Some appear as flattish shapeless drops, but
others take more elevated forms, like sacks set on end, and usually
displaying two mouths. One of these is of a pellucid yellowish green,
or olive hue, with a cloudy spot of rich orange in the interior. A
slight shrinking from the touch, a yet closer contraction of the
projecting points, is the only token of life that we can discern in
it now; but if we place it in an aquarium,--not forcibly removing it
from its attachment, but lifting the shell or stone on which it rests;
or, if this be too large, detaching the fragment with a chisel,--and
allow it to remain a few hours undisturbed, we shall see evidences of
a vitality, indubitable if not very active.
The whole creature is now much plumper and more pellucid; it stands
up boldly from its base on the stone; its upper portion is much
lengthened, and the two wart-like eminences have become two short
tubes with gaping extremities, appearing as if they had been soldered
together side by side, of which the one is considerably higher than
the other.[149]
We have before us one of the _Tunicata_, an order of molluscous
animals which are closely allied to the _Conchifera_ or bivalves, but
somewhat lower in the scale than they. It has no shell; that is to say,
lime is not deposited in the outer investment, so as to give it the
hard, rigid, solid texture of shell; but the internal organs, which
are essentially similar to those of an Oyster or a Sand-gaper, are
enclosed in a tough leathery coat, known as the _test_, which is in
fact a closed shell destitute of lime. The eminent physiologist, John
Hunter, who had dissected some of these homely Squirters, as they are
familiarly called, recognised, with his wonted acumen, the structural
similarity of their leathery envelopes to the stony shells of the lower
bivalves; and, associating them in a group, called them “soft-shells.”
The naturalness of this group, since called _Tunicata_ by Lamarck, has
been recognised by modern zoologists.
[Illustration: