But there are more things than shrimps in the gleaming, working,
struggling mass of life before us. Not to mind the uncouth
soldier-crabs, dragging about their despoiled shells, which, numerous
and conspicuous as they are, we shall neglect for another occasion,--we
have other fish to fry. Here are sundry examples of that remarkable
race, the proper Flat-fishes. These thin, brown, long-oval ones are
specimens of Soles, of which there are two kinds here, the Common Sole,
uniform dull brown, and the Lemon Sole, of a more freckled tint, pale
orange brown, with darker spots.[54] The fisherman considers them
marketable if they are not less than four or five inches long, and
bundles them into his common depository, under the title of tea-dabs,
a name which sufficiently indicates their destiny.
Now every one has looked at hundreds of pairs of soles raw and ready,
but perhaps not all have ever adequately remarked the singular anomaly
presented by their structure, or are aware how unique their tribe is
among animals. That one surface is positively coloured, while the other
is fleshy white, is no great matter; for many creatures, and fishes in
particular, are darker above and paler below. The flat Rays are equally
abject, and show a like contrast of hues; but, _structurally_, the
colours in the Sole are not respectively on the back and belly, though
they are certainly above and below. These fishes, in fact, swim and lie
_on one side_; and so they have one side dark and one side light.
This habit, however, imposed upon them, involves other very important
aberrations from ordinary forms. Let us suppose that the eyes had been
placed, like those of the Chætodons (very thin, wide, and flat fishes
of the tropical seas), one on each side of the head. That eye which
belonged to the white or inferior side, would be rendered useless,
since it would be almost perpetually buried in the mud of the bottom.
Hence, by an unprecedented exception to the symmetry which marks the
organs of sense in all other vertebrate animals, both of the eyes are
placed on the same side of the head, one above the other. They are,
however, frequently not in the same line, and one is often smaller and
less developed than the other.
In addition to these peculiarities, we may remark, that the spine makes
a sudden twist near the head to one side; that the bones of the head
are not symmetrical; that the two sides of the mouth are unequal; that
the pectoral and ventral fins of the under side are generally smaller
than those of the upper; and that the dorsal and anal fins generally
correspond to each other, the one fringing the whole length of the
dorsal, the other that of the ventral edge of the body.