THE Soft-bodied animals, to which the term "Mollusca" is applied, constitute another of the primary groups of the animal kingdom. In them we see no longer the jointed structure, which characterised the crustacea and insects. The arrangement of the nerves is also different; and the blood is colourless or not red.

The beautiful variety of form observable in the shells of

different species of Mollusca (Fig. 105, 106, &c.), has, in all ages, attracted attention; and the splendour of their colouring is not surpassed by that of our brightest gardenflowers. In some respects it is even superior; for their most

delicate tints become here unfading and permanent, and a peculiar structure of the surface gives rise occasionally to rainbow hues. Among savage tribes, shells are formed into ornaments, and applied to numberless uses.

500 pounds; from which circumstance the story may have

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originated of an oyster which furnished a dinner to a whole regiment. Let us, in imagination, contrast with this the microscopic shells collected by Soldari in Tuscany, and which were so minute, that numbers of them passed through a paper in which holes had been pricked with a needle of the smallest size.

The change of form which shells undergo, as they approach maturity, is sometimes so great, that the full-grown specimen is altogether different from the appearance presented by the same shell in its immature state. Of this the common Leg-of-mutton Shell (Fig. 108) of our shores, and the beautiful tribe of Cypræas (Fig. 109), furnish familiar examples.

PES PELICANI.

those which, like the snail, are provided with a head, and generally with mouth, eyes, and tentacula, or feelers. Each of these groups is divided into three Classes, to which our attention may now be directed.

THERE are some Mollusks which are not naked like the slug, nor provided with a shelly citadel like the oyster, but are furnished with a kind of leathery covering or tunic, and are hence termed "Tunicated." The kind best known to our fishermen is a solitary species about the size of the largest common mussel, and to which, from its shape, the name of "paps" is given. The exterior is darkish, warty, and unattractive, and exhibits two orifices, from one of which the animal can squirt water with considerable force. The internal structure is extremely beautiful and delicate. Some of the compound species are branched (Fig. 110), and such is their transparency that the movement of the internal organs can be distinctly seen.

Fig. 110.-m, Mouth.-s, Stomach.-i, Intestine.-o, Orifice.-t, Common Stem. The arrows indicate the direction of the currents of water subservient to respiration.

THESE are Mollusca, with two shells (bivalve), and, like some of those just mentioned, are destitute of the power of locomotion. They are attached to foreign bodies, and are furnished with two long arms (Fig. 111), covered with the minute hair-like bodies termed cilia, which have been already described (p. 12, 25, 30). They are found abundantly in a fossil state. The species now existing are few in number, and some of them have been brought up from depths of from sixty to ninety fathoms. In the unbroken stillness which must pervade these abysses there can be neither wind nor waves to bring to them the animalcules which they require as food, or to sweep away what would become injurious. Their very existence must therefore depend on their power of producing a perpetual current around them, which they are enabled to effect by the action of the cilia, though organs of such apparent delicacy.