by which their life is supported and their kind continued, as in the animals themselves; and yet in all this diversity should trace a harmony and concatenation that would evidently prove the Wisdom that contrived, the Power that formed, and the Goodness that gave a living principle and breath of life to all these creatures, were each of them the attributes of an INFI-.

NITE BEING.

17*

CHAPTER VIII.

Functions and Instincts. Bivalve Molluscans.

HITHERTO in our progress from the lowest animal upwards, the mind has been perpetually submerged; not only every group, but every individual that we have had occasion to consider, has been an inhabitant of the waters, and to the great body of which a fluid medium is as necessary to life and action as an aërial one is to a land animal, but now we shall be permitted to emerge occasionally, for although the largest proportion of the animals forming the great class we are now to advert to, the Molluscans, are also aquatic, yet still a very considerable number of them are terrestrial, as a stroll abroad will soon convince us, when after a shower we find we can scarcely set a step without crushing a snail or a slug.

The term Molluscan1 was employed by Linné to designate his second class of worms, which excluded all the shell-fish, and amongst real Molluscans included both Radiaries, Tunicaries, and Worms; it literally signifies a nut or walnut, and therefore seems more properly applied to shell-fish, than to animals which are defined as simple and naked. As now understood, it still comprehends a very wide range of animal forms, and it seems difficult to describe them by any character common to them all. Their Almighty Author, in the progress of his work of creation, linked form to form in various ways; he not only made an animal of a lower grade a stepping-stone towards one of a higher, and which formed a part of the ascent to man, the highest of all; but as the mighty work proceeded, he threw out on each side collateral forms that ascend by a dif ferent route, or begin one to a different order of beings. And this circumstance it is that has opened the door for so many systems and that diversity of sentiment with respect to the grouping of animals, which we meet with in the writings of the most eminent naturalists. Some proceed by one path and some by another, though the object of all is the same,

1 Mollusca.

2 Vermes.

unless some bias from a favourite hypothesis interferes and diverts them from a right judgment.

The organization of the animals of the Class we have just left, as we have seen, appears of a higher character than that of any of the preceding ones; traces of a heart appear; a nervous ganglion is detected between the mouth and anus, sending nerves to each; a regular respiratory system by means of gills becomes evident; but still the animal is furnished with no head, no eyes, and in numerous cases has no separate existence, but forms a branch of the general body-thus resembling a plant-from which it cannot dissociate itself and become an independent individual.

Indeed when we enter the Class of Molluscans, we find that the nearest affinities of the Tunicaries have likewise no head, and this circumstance appears to have induced Lamarck not only to separate them from the class as arranged by Cuvier, but also his whole family of headless Molluscans,' of which he forms his two Classes of Cirripedes and Conchifers.3 The absence of a head from the animals of the bivalve and multivalve shells, is certainly a circumstance which, at the first blush, appears to justify their separation classically from the other Molluscans, but when we compare other characters, we shall find many that are common to both, particularly their nervous system, which is the same both in the Conchifers and Molluscans of Lamarck; for neither of these exhibit a medullary ganglionic chord, but only dispersed ganglions which send forth the requisite nerves; both have a double or bilobed mantle, gills on each side, and a heart and circulation. The Cirripedes indeed seem to be of a higher grade, at least their nervous system is more perfect-since they have a longitudinal spinal marrow with ganglions, a mouth furnished with toothed jaws disposed by pairs, and jointed tendril-like organs about the mouth-and approaches near to that of the Annulose animal,♦ the Condylopes of Latreille. These, therefore, may be considered as properly entitled to the denomination of a Class; but should not be placed at a distance from the Crustaceans, to which Lamarck, with reason, thinks they make a near approach, as they are by Cuvier and Carus. In fact, they seem to have little to do with the bivalve Molluscans, except in being defended by more than one shell, and having no head.

I shall now mention the most prominent characters of those

1 Mollusca acephala.

3 Conchifera.

2 Cirripeda.

4 Annulosa.

shell-fish, that I regard as strictly entitled to the denomination of Molluscans.

ANIMAL Soft, without articulations. Mantle bilobed, enveloping more or less the animal. Gills varying. A heart and circulation. No medullary chord with ganglions, but a few scattered ganglions from which issue nerves to various parts. Body commonly defended by a calcareous shell, to which it adheres only by one or two points, but in some instances it is externally naked, and has an internal bone.

The Molluscans may be divided into several families, and those of Cuvier are mostly natural, but as my plan has been to ascend from the lowest grade of animals towards the highest, I shall reverse this order, and begin my observations with the last of his families, or more properly speaking Orders, excluding for the present the Cirripedes of Lamarck, or most of the multivalves of Linné, as leading off laterally towards the Crustaceans.

His first order he calls Acephales, or headless Molluscans, it includes all the bivalve shells of Linné, with the addition of the Pholads or stone-borers.1 Lamarck has divided it into two sections, which, regarding it as a Class, are with him Orders; the first is Bimuscular, having two attaching muscles, and two muscular impressions; and the second is Unimuscular,3 having only one such muscle with one impression. With regard to their habits and economy, the bivalve molluscans may also be divided into two sections, the first of which may consist of those that enclose themselves either in a cell or burrow, or live in the mud, &c.; and the second of those that fix themselves to the rocks, stones, and other substances, by means of a Byssus, which they have the faculty of spinning from their foot or other part, or by a tendinous ligament which they protrude through an orifiee in their shell.

The general habit of the first family, including a vast variety of forms, seems to be that of boring and burrowing, many piercing wood, and even rock, and others burrowing in the sand, sometimes to a great depth. Thus they are instructed by their instinct to form a convenient cell or other habitation, either constantly submerged, or only when the tide visits them, in which they are enabled to procure their destined food, of what nature does not appear to have been clearly ascertained, although probably animalcules, introduced when they inspire

1 Pholus.

3 C. monomyaires..

2 Conchifères dimyaires.

the water for respiration, may form a principal portion of it, as the majority having no teeth for mastication, require a kind of nutriment for which it is not necessary: comparing this tribeof aquatic animals with those of the antecedent classes, we see the same object effected by different means. The sheathed polype' builds a house of matter elaborated in its own stomach, while the ship-borer pierces wood, and the stone-borer the rocks, and the razor-shell3 burrows deep in the sand with the same view; and thus each is instructed by its Omniscient Creator, and fitted by its structure and organization, to accomplish the intended purpose, but by different means and instruments.

While each of these creatures has a particular and individual end in view, in its several proceedings, its own accommodation and appropriate nutriment and defence; the Creator, who has gifted them accordingly, makes use of them as instruments, which by their combined agency, though each, as it were, by a different process, accomplish, usually by slow degrees, His general purposes. This object, in the present instance, as well as in numerous others, seems to be to remove obstacles that stand in the way, and prevent certain changes willed by Providence, in the sea-line of any country, from taking place. Rocks may be regarded as so many munitions of a coast, which prevent the encroachment of the ocean, but nothing can more effectually prepare the way for the removal of this safeguard, than its being, as it were, honey-combed by numberless stone-borers, that make it their habitation, thus it must be gradually rendered weaker; till it is no longer able to resist the impetus of the waves; the process is very slow, but it is sure; and it is worthy of remark, by what a seemingly weak organ most of these animals are enabled to effect this purpose, a fleshy foot, strengthened by no internal bone or gristle, but upon which they can turn as upon a pivot, and so in due time effect their destined purpose.

I shall now proceed to furnish some examples of the manner in which this is effected: and give an account of some of each of these tribes, beginning with those, and they are numerous, that make the burrows in the sand to a considerable depth, so that it presents a less solid mass to the action of the waves.

I shall first call the reader's attention to the proceeding of one usually denominated the razor-shell, from the supposed resemblance of some of the species to that instrument; in substance and colour they are often like the human nail, and as

1 See above, p. 89, n. 2.

2 Teredo.

3 Sulen.