There is a curious peculiarity in the eye of this fish, which I do
not perceive in the Shanny, nor in any other species. On looking
cursorily at it, you would suppose that it had a very widely-opened
pupil, surrounded by a white line, which appears to be the interior
edge of the iris. But on watching it with a lens, the whole of this
dark area within the white circle is seen to be prominent, convex, and
opaque, of a substance which reflects the richest metallic lustre,
sometimes turquoise blue, but changing in other lights to a bronzed
or gilded appearance; not, however, as if burnished, but as if dusted
with metal filings. In the centre of this area a pupil alternately
opens and closes, expanding and contracting circularly, with a regular
systole and diastole, a little more quickly than the periodic opening
and shutting of the gill-covers, but nearly corresponding therewith.
The contraction of this pupil is perfect, so as completely to conceal
it, and the expansion is irregular in extent, though regular in time;
sometimes it is but just perceptible, when the next opening will be as
wide as usual. Occasionally, the motion ceases, the area displaying no
trace of a pupil.
Mr. Ross of Topsham, an excellent marine zoologist, has observed a
highly curious habit in the commonest of the Blennies. It is the Smooth
Shan, Shanny, or Tansy,[110] of our southern shore-bays. I was aware
that these little fishes were capable of enduring with impunity a
protracted exposure to the air, which would be fatal to many, but I did
not suppose that the habit was normal and constant. The facts reported
are of great interest.
“A specimen of the fish,” says Mr. Ross, “was brought to me on the 3d
of June. On placing it in a glass vessel of sea-water, it appeared
perfectly quiet for some hours, but at length became restless, and
made frequent attempts to throw itself out of the water. It then
occurred to me, that on a former occasion, when by the sea-side, I had
a Gattoruginous Blenny, in a vessel with some Actiniæ and Serpulæ,
which regularly passed a portion of its time on a stone; I therefore
placed one in the glass. The _Blennius pholis_ immediately leaped on it
completely out of the water. It therefore appears that these changes
are necessary to its existence. On going to the front of the house, I
perceived that it was near low water. Knowing that it would flow till
ten o’clock that night, I watched the movements of my little captive,
and as the clock struck, had the gratification of seeing it plunge
again into its natural element. It has now been more than five months
in my possession, and has proved throughout that period a regular and
correct tide-indicator. I was well aware that these fish are constantly
left by the receding tide on the rocks, remaining concealed in small
basins or holes, under the weed, till the returning flood; still I
was not prepared to see a fish voluntarily quit the water, and pass
so large a portion of its existence in a different element, and by
instinct alone time its change of position so exactly.”[111]
This is a highly curious observation; but, as to Mr. Ross’s inference
that “these changes are necessary to its existence,” I may remark that
I have been in the habit of keeping the Shanny for long periods in my
tanks, without any opportunity for such alternations.