sizes and shapes, chiefly five- and six-sided, and all having one or more elevated points near the centre. These crystals are imbedded in the surface of the boring foot and thickened edges of the mantle; and, consisting, probably, of silex or flint, either pure or in combination with some animal matter, they form a sort of file—superior, however, to any of our workmen's files in this, that the surface keeps itself always in a proper state of roughness for trituration. This is done by an organic law, which causes the crystals to be constantly shed, and as constantly renewed.[17]
LIMPET.
All the borers above alluded to are Bivalves, and I know of no other Mollusk which can properly be classed with them. A common Gasteropod, however, the familiar Limpet (Patella vulgata), excavates the rock on which it lives to the extent of making a depression, more or less deep, exactly corresponding to the shape and size of the margin of its shell. When one removes a Limpet from its firm adhesion and finds a hollow beneath it, evidently made to contain its body, one is ready to conclude that the animal is a permanent tenant of the spot, never moving from it; and when we learn that the food of the Limpet consists of sea-weeds, we wonder how it is possible that a stationary animal can find vegetable food. But the truth is, I believe, that the Limpet wanders away from its hollow during the night, returning to it as a home by an infallible instinct on the approach of morning. The mode in which the excavation is performed is the same as that just mentioned in the case of the borers, the whole under surface of the foot being furnished with sharp crystals of flint imbedded in its substance.
In general the stony shells of the Mollusca afford them, a sufficient protection, but a few species construct for themselves nests. A native example of this instinct is described in interesting terms by the Rev. D. Landsborough, who obtained it in Lamlash Bay:—
"The most interesting, though not the rarest, thing we got was Lima hians. I had before this some specimens of this pretty bivalve, and I had admired the beauty and elegance of the shell; but hitherto I had been unacquainted with the life and manners of its inhabitant. Mr. and Miss Alder had got it in the same kind of coral at Rothesay, so that when Miss Alder got a cluster of the coral cohering in a mass, she said, 'O, here is the Lima's nest!' and breaking it up, the Lima was found snug in the middle of it. The coral nest is curiously constructed, and remarkably well fitted to be a safe residence for this beautiful animaL The fragile shell does not nearly cover the Mollusk, the most delicate part of it, a beautiful orange fringe-work, being altogether outside of the shell. Had it no extra protection, the half-exposed animal would be a tempting mouthful—quite a bonne-bouche to some prowling haddock or whiting; but He who tempers the wind to the shorn lamb, teaches this little creature, which He has so elegantly formed, curious arts of self-preservation. It is not contented with hiding itself among the loose coral, for the first rude wave might lay it naked and bare. It becomes a marine-mason, and builds a house or nest. It chooses to dwell in a coral grotto; but in constructing this grotto it shows that it is not only a mason, but a rope-spinner, and a tapestry-weaver, and a plasterer. Were it merely a mason, it would be no easy matter to cause the polymorphous coral to cohere. Cordage, then, is necessary to bind together the angular fragments of the coral, and this cordage it spins; but it spins it as one of the secrets of the deep. Somehow or other, though it has no hand, it contrives to intertwine this yarn which it has formed, among the numerous bits of coral, so as firmly to bind a handful of it together. Externally, this habitation is rough, and therefore better fitted to elude or to ward off enemies. But though rough externally, within all is smooth and lubricous, for the fine yarn is woven into a lining of tapestry, and the interstices are filled up with a fine slime, so that it is smooth as plaster-work …
"When the Lima is taken out of its nest, and put into a jar of sea-water, it is one of the most beautiful marine animals you can look upon. The shell is beautiful; the body of the animal within the shell is beautiful; and the orange fringe-work, outside of the shell, is highly ornamental. Instead of being sluggish, it swims about with great vigour. Its mode of swimming is the same as that of the scallop. It opens its valves, and, suddenly shutting them, expels the water, so that it is impelled onwards or upwards; and when the impulse thus given is spent, it repeats the operation, and thus moves on by a succession of jumps. When moving through the water in this way, the reddish fringe-work is like the tail of a fiery comet.
LIMA.
The filaments of the fringe are probably useful in catching its prey. They are very easily broken off, and it is able that they seem to live for many hours after they are detached from the body, twisting themselves like so many worms."[18]
Thus we have slightly touched a few of the details of the history of this great division of animated beings; and we discover that they are not less rich in interesting endowments and faculties, in various contrivances and compensations, in singular habits and instincts, than other animals higher in the scale of organization. But it is only when we study the Mollusca as living beings, that we discover these points of varied interest. The mere collection of shells, however curious their forms and brilliant their colours, would impart but a small amount of knowledge when separated from the animals to which they belong. "The shell-collector of former days looked upon his drawers, if they were rich in rare species or varieties, as containing an assemblage of gems; and, indeed, the enormous prices given for fine and scarce shells, joined with the surpassing beauty of the objects themselves, almost justified the view which the possessor took of his cabinet of treasures. They were to him really 'les delices des yeux et de l'esprit;' and the energetic zeal with which he collected, and the sacrifices that he made to procure a fine and perfect Many-ribbed harp, a Gloria maris, or Cedo nulli, among the cones; an Aurora or Orange-cowry, a Voluta aulica, or Voluta Junonia, &c., were only comparable to the extravagances of those visited by the tulip mania when it was at its height. But though they were the delight of his eyes, they were, in nine cases out of ten, little more to the owner of them: they were mere trinkets on which he looked dotingly, without knowing, and scarcely wishing to know, the organization of the animal whose skeleton only was before him."[19]
In these days, however, the examination of the shell is considered by all who possess any claim to science, as subordinate to the history of the entire animal.
Naturalists arrange the Mollusca in six classes, named Cephalopoda, Pteropoda, Gasteropoda, Conchifera, Brachiopoda, and Tunicata. Of these the first three are sometimes distinguished as Encephala, or furnished with a head; the last three as Acephala, being destitute of that organ.
1 ↑ That is, "having dissimilar nerve-knots."
2 ↑ Zool. Journ. iv. 172.
3 ↑ Introduction to Conchology, p. 199.
4 ↑ Introduction to Conchology, p. 173.
5 ↑ Jones's Animal Kingdom, p, 385.
6 ↑ Johnston's Conchology, p. 134.
7 ↑ Annals of Natural History. October, 1852.
8 ↑ Johnston's Intr. to Conch. p. 125.
9 ↑ Philos. Trans.