The internal dweller in the front parlour is the Hermit Crab (Paguras Prideauxii), a creature seldom contented with its own pretty solid habitation, but ever seeking some further protection, which it generally finds in an empty Whelk-shell. It is, moreover, very particular as to fit, and other details; for it has been observed, when looking out for a house, to try and reject many before finally adopting an abode. The inhabitant of the back parlour is the Sea-Worm, Nereis bilineata, a creature which, instinctively knowing the voracious propensities of the Crab, and determining to share his abundant feasts, seizes his opportunity, when mine host of the Whelk-shell is pretty well surfeited and in a semi-dormant state, to sneak past the dangerous claws into the “back parlour,” which is the interior of the narrow spiral of the shell—a form of apartment which affords him a most comfortable and convenient home, in which, by the superfluous voracity of the Crab, he is furnished with board as well as lodging. The external tenant of the Whelk-shell is a parasitic Sea-Anemone, known as the Cloak-Anemone, from its power of nearly enveloping the object to which it attaches itself, by means of the extension of its stem or body. It is known in scientific classification as Adamsia palliata, having been made a separate genus, and its specific name ingeniously taken from that of the Roman cloak, the well-known pallium of the classical writers.
Almost invariably, when the Hermit Crab is discovered inside the Whelk-shell, the Adamsia is found outside; and the Hermit is seldom without his dinner assistant, the prettily-striped Nereis. This fact is so well known to fishermen, that when in search of this worm, which is an excellent bait, they never fail to break the shells tenanted by the Hermit Crab, and are seldom disappointed in finding the object of their search in his company.
Another parasitic Anemone, still more fond of travelling, the Actinia parasitica, often selects the back of the Crab himself (generally Paguras Bernhardus), and in that position is hurried along, in the sidling gallop of his steed, in a way that must often prove inconvenient; for in passing under ledges of rock, the Crab, doubtless, only takes his own measure. Yet, in such cases, the Anemone probably knows how to take care of himself; and when Bernhardus becomes skittish and adventurous, “draws in his horns,” as many other bold spirits are obliged to do at certain crises of their career; and in this state, presenting only a semi-spherical mass of tough leathery substance, he can fearlessly allow himself to be driven beneath stony archways, or under impending branches of the marine forests, by his ferocious Jehu, with less chance of injury than the outside passenger of a terrestrial stage-coach passing beneath the low gateway of some inn-yard.
Our largest native shell of the Whelk tribe is the Fusus antiquus, often used by the Shetland islanders as a lamp; for which purpose it is suspended horizontally, the cavity holding the oil, and the wick projecting from the canal.
The Whelks belong to the interesting family Muricidæ, some of which, natives of our own coasts, are very pretty objects for the Aquarium. It was the Murex trunculus which yielded the Tyrian purple, different species affording distinct tones of colour. In form, these shells are somewhat like our common Whelk, but finely marked with broad, dark, spiral stripes. The ancient mode of extracting the dye, as described by Pliny, was verified by Mr. Wild, in 1838, in a very interesting manner. In the neighbourhood of the site of the ancient Tyre, he found, in the rocks on the sea-shore, a vast number of round cavities, evidently the work of the hammers and chisels of long ages past. These cavities varied in size, from that of a small flower-pot to that of a cauldron, and round about them still lay scattered immense masses of the remains of the shells and bodies of the Murex, in many instances aggluminated together. They had evidently been pounded in those cavities, exactly as described by Pliny, and the dye extracted according to the formulæ so graphically detailed by the ancient naturalist.
The Purpura lapillus of our own shores yields a similar dye, and may be kept in our Aquaria as a reserve bottle of “marking-ink;” for the ingenious Mr. Gosse has shown how its dye may be thus used for household purposes. The shell is a small white univalve, with one or more bands of pale brown. It perishes on being immersed in fresh-water; and a thick vein of yellowish white, near the head, contains the dye, which is a liquid of a creamy thickness and of pale, indistinct colour. But if it be painted in the forms required, as a cipher, or any other ornament, on linen, or any other textile fabric, with a camel’s-hair pencil, and exposed to the air, it rapidly assumes a yellow tone; which first changes to green, then blue, till at last it becomes a full strong indigo, exhibiting plainly all the forms that have been traced. A crimson-red change next ensues, and the final colour, which is indelibly permanent, is a reddish purple.
There is also a large naked Mollusc, one of the Aplysia, that pours forth, under excitement, a secretion of rich purple hue; but the colour is considered valueless as a dye, from its extreme volatility, though it is stated that it may be rendered permanent by means of nitric acid.
The common Planorbis corneus, a shell coiled in the form of a ram’s horn, has a similar property; but the colour of the fluid is still more volatile. The purple liquid, however, contained in another of our native shells (Scalaria) is very permanent.
It is well known that the ink of the Chinese, which we term Indian ink, is prepared from the Cuttle, and the Cuttles of the Mediterranean Sea furnished the principal black inks and dyes of the Greeks and Romans. It is a kind of Sepia, in fact, that still furnishes the rich brown colour which bears the name of the animal from which it is derived.
The common Sepia vulgaris might form an appropriate specimen for a marine Aquarium, many of its habits being singular; and its power of enveloping itself in a cloud of its own rich dye may often be observed when it is irritated by the presence of a real or fancied danger. It has the faculty of propelling itself hither or thither by the emission of a jet of water, as described in speaking of the locomotive power of other Molluscs, with the additional faculty of guiding its motions by the rapid movement of two fin-like paddles, which, when in agitation, produce an effect not unlike the fluttering action of the wings of a moth. This little Cephalopod has large projecting eyes, and a group of arms that hang listlessly down when the fins are in motion. It changes colour fitfully and beautifully, exhibiting in the course of such changes pretty metallic spots and rings, which appear and disappear, now like gold, now like silver, as seen through a semi-opaque substance. The whole creature is at one moment of a dusky gray tone, but fitfully changes to white or deep brown when alarmed. These little creatures are exceedingly voracious, and when one was observed by Mr. Gosse to seize another of its own species, the victim shot out its defence of dark black fluid.