To premise:--the Cloaklet is an anemone of the _Sagartia_ family,
beautiful in its colours and remarkable in its form. It is generally
reddish-brown on the outer (lower) part of its body, which hue melts
into snowy white on the upper parts; the whole studded with rosy-purple
spots, and surmounted by a marginal line of pale scarlet. The tentacles
and disk are pure white. It attains a rather large size, and has
the peculiarity of being not round in its basal outline like other
Anemones, but oblong, the base expanding in two lateral directions.
It always selects the inner lip of an univalve shell for its place of
adhesion, and the two lateral ends of its base gradually extend around
the mouth of the shell till they meet on its outer edge, and unite with
a suture: thus the outline of the animal forms a ring.
It had often been an interesting speculation with me, in what manner
the due relation of size is maintained between the _Adamsia_ and the
shell, in the progressive growth of the former. There is a manifest
proportion between the two, the young Cloaklet occupying a small shell,
such as that of a _Littorina_ or _Trochus_; the full-grown individual
a large one, such as that of a _Natica_ or _Buccinum_. The Crab is
able to shift from a smaller to a larger shell when he needs enlarged
accommodation; and since we know that his congener, _P. Bernhardus_,
does this habitually, we naturally conclude that such is the habit of
_P. Prideauxii_. Presuming then that this is the case, what becomes
of the _Adamsia_? If the Crab shifts his quarters and leaves the
_Adamsia_ behind, the association is broken, and we should constantly
find _Paguri_ without _Adamsiæ_, and _Adamsiæ_ without _Paguri_. But we
find neither the one nor the other.
On the other hand, if _Adamsia_ is able to shift its quarters also,
how does it proceed in its search for a new shell? If it forsakes the
old tenement at the same time as the Crab, and together with it takes
possession of the new one, by what means is unity of will and action
secured? What communication of thought takes place from the one to the
other? As the _Adamsia_ does not adhere to the Crab, but to the shell,
that is, as they are independent of each other’s movements, who takes
the initiative? Who goes to seek the lodging? And at what point of the
transaction does the other come in? All these questions I had mused
upon with interest; and at length received some light towards their
solution.
On the 10th of January, 1859, I obtained, by dredging, in Torbay, a
specimen of _Adamsia palliata_, about half-grown, on a rather small
shell of _Natica monilifera_, tenanted by a _Pagurus Prideauxii_, which
seemed already too big for his habitation. Having put them into a
well-established tank of large dimensions, the contents of which were
in excellent condition, I succeeded in doing what I had never done
before, domiciliating both Crab and _Adamsia_. Both continued in the
highest health, and became quite at home.
After about three months, however, I noticed that the _Adamsia_ was
not looking so well. One side or wing had gradually loosed its hold of
the shell-lip, so that it hung loosely down beneath the breast of the
Crab. Yet in other respects the zoophyte seemed healthy. Latterly, too,
the Crab had manifested symptoms of uncomfortable straitness, in the
great extrusion of his fore-parts; so great, indeed, as to expose even
the front of the soft abdomen. Yet I felt reluctant to present to the
Crab a larger shell, fearing that he would, in availing himself of it,
desert his zoophyte friend, which would then die, and I should lose the
specimen.
At length the desire to solve a problem in science prevailed over this
feeling. A fact is better than a specimen. And so (on April 21st) I
selected from my cabinet a full-grown _Natica_ shell, and placed it on
the tank-floor, not far from the disconsolate trio.
The _Pagurus_ presently found the new shell, and immediately began to
overhaul it. He did not do, however, as his brother Bernhard would have
done, at once shift into the new house. Having turned it mouth upward,
he took hold of the outer and inner lip, each with a claw, and began
to drag it about the tank. Occasionally he relinquished the hold of
one claw, and probed the interior in the usual manner, and then resumed
his march. I watched the proceedings for an hour or more, when, having
other work to do, I left him alone.
The thought did occur to me--Can this delay be intended to make the
_Adamsia_ cognizant of what is in contemplation, and to prepare it for
the change? But I dismissed it as unlikely.
After about an hour’s absence I returned to the examination. The
_Pagurus_ was comfortably lodged in his new abode, and the old one,
which now looked small indeed, lay deserted at some little distance. I
eagerly turned the latter over, to see what was the condition of the
_Adamsia_. Lo! no _Adamsia_ was there; and the _Pagurus_, presently
approaching the front of the tank, I saw, to my great gratification,
that the old association was unbroken. There was the _Adamsia_, with
one wing adhering to the lip of the new shell, and apparently the
opposite wing also; but, from the position of the group, this I could
not be quite certain of. The situation of the zoophyte was quite
normal,--the centre immediately below the breast of the Crab, and in
contact with the inner lip of the shell, while that wing which I could
clearly see was creeping round upon the outer lip.
Examining now more closely the condition of things, with a lens, I saw
that the central part of the _Adamsia’s_ base was adherent by a small
point of its surface to the under side of the thorax of the Crab,
between the bases of the legs.
Now this adhesion to the Crab is a circumstance which, so far as I
know, never takes place in the ordinary relations of the animals; and
therefore I could not but think it an extraordinary and temporary
provision for the removal of the _Adamsia_ from the old to the new
shell, and for the correct adjustment of its position on the latter.
How then can we avoid the conclusion, that, as soon as the Crab had
found the new shell to be suitable for exchange, the _Adamsia_ also
was made cognizant of the same fact; and that, during the two hours
which followed, the latter loosened its adhesion to the old shell, and,
laying hold of the bosom of its protector, was by him carried to the
new house, where immediately it began to secure the like hold to that
which it had just relinquished?
Eleven days elapsed after the above observations were made, when I
obtained another interesting fact bearing on this strange association.
The _Adamsia_ had not looked well since the change of residence; its
adhesion to the shell had been but partial at the best, some days
more, some days less, extensive; but for the most part a considerable
portion of the zoophyte was hanging down from the shell. The Crab, on
the other hand, was evidently in clover, and showed no inclination to
go back to his old lodging.
On the 2d of May I found the _Adamsia_ detached, and lying helpless on
the bottom of the tank, beneath the Crab, who, when disturbed, walked
off, leaving his companion behind. I thought now it was a gone case,
and that it was all up with my elegant _protegée_.
An hour or two afterwards, however, how great was my surprise to see
the _Adamsia_ fairly established again, adhering to the shell by a
good broad base, and looking more healthy than I had seen her for many
a day! Strangely enough, she was adhering in a false position, having
taken hold on the outer lip of the shell, instead of the inner, as
usual. Here was a fresh proof of intelligence somewhere; and I at once
set myself to find where.
Carefully taking up the shell with the aquarium-tongs, and bringing
it close to the surface, but not out of water, I gently dislodged
the _Adamsia_ with my fingers, and allowed it to fall prone upon the
bottom. I then released the shell with its tenant, and drove the latter
towards the spot where the zoophyte lay.
No sooner did the Crab touch the _Adamsia_ than he took hold of it with
his claws, first with one, then with both, and I saw in an instant what
he was going to do. In the most orderly and expert manner he proceeded
to apply the _Adamsia_ to the shell. He found it lying base upward,
and therefore the first thing was to turn it quite round. With the
alternate grasps of the two pincer-claws, nipping up the flesh of the
_Adamsia_ rudely enough, as it seemed, he got hold of it so that he
could press the base against the proper part of the shell, the inner
lip. Then he remained quite still, holding it firmly pressed, for about
ten minutes; at the end of which time he cautiously drew away first
one claw, and then the other; and, beginning to walk away, I had the
pleasure to see that the _Adamsia_ was once more fairly adhering, and
now in the right place.
Two days after the _Adamsia_ was again lost. On searching I discovered
it lying in a crevice, whence I plucked it, and laid it on the bottom.
Here again the Crab found it, and immediately went through the same
process as last described, and again made it adhere. But I saw that
the _Adamsia_ was unhealthy, for it seemed to have but enfeebled
power of retaining its hold. The manifestation of the mode in which
the instinctive actings of the two creatures occur is, however,
sufficiently clear. The Crab is certainly the more active promoter of
the partnership; it is abundantly evident that he values the company of
his elegant but very heterogeneous associate. These last observations
compel the conclusion that the claws of the Crab are always employed in
the transference of the Cloaklet from shell to shell.[122]