the advancing tide has again covered them, they are roused to more active life,-unfold their tentacula, and present the appearance of expanded flowers.

Though found attached to the rocks, they are not fixed there permanently, but can change their place at pleasure. Some species are used as food by man, and, when boiled in sea-water, are said to have both the smell and taste of lobster. They live upon small aquatic animals of every kind, including crustacea and shell-fish; the hard and indigestible parts being rejected by the mouth, about ten or twelve hours after being swallowed.

Perhaps no fact connected with these animals is more remarkable than their power of bearing mutilation. If the tentacula be destroyed, others are soon after formed. If the animal be cut across into two distinct portions, the upper part continues to take food as usual, though for a time unable to retain it; if divided in the opposite direction, two Sea-anemones are produced; and if only a part of the base be left, a perfect animal is soon raised up.

Dr. Johnston, the learned author of a work on the British Zoophytes, mentions a characteristic occurrence respecting a Sea-anemone which had been brought to him. It might have been originally two inches in diameter, but had somehow contrived to swallow a scallop shell the size of an ordinary saucer. The shell fixed within the stomach was so placed as to divide it completely into two equal parts, so that the body stretched over it had become thin and flattened

like a pancake. All communication between the mouth and the interior of the stomach was of course prevented, but the animal, instead of dying of starvation, took advantage of the accident to increase its enjoyments, and its chance of double fare, for a new mouth furnished with tentacula was opened up on what had been the base, and led directly to the lower stomach.

Belonging to the same order, but to a different family from the Sea-anemones, are the Coral-building Polypes of

tropical seas (Fig. 13). Their structures have been the wonder of the navigator and the theme of the poet; and while science endeavours to reveal the process by which they are upreared, she brings forward another example that, under the dispensation of Providence, the mightiest of works can be executed by the weakest of agents.

It was formerly supposed that the Coral-building Polypes worked in unfathomable depths, and in the course of ages reared their pile to the surface of the water; but recent and widely extended observations have shown that this is not the case. The species most efficient as Coral-builders work only at limited depths, not exceeding twenty or thirty fathoms. Yet their labours, taken in connection with geological changes, are sufficient to produce reefs in the Pacific of several

hundred miles in length. These structures, it must be remembered, are not formed in an expanse of deep and tranquil waters, but in the midst of an ocean which is never at rest. "The breakers," as Mr. Darwin remarks, "exceed in violence those of our temperate regions; and it is impossible to behold them without feeling a conviction, that rocks of granite and quartz would ultimately yield and be demolished by such irresistible forces." Yet these coral islets stand uninjured, for here another power comes into operation. The particles of lime contained in the seawater, are separated from it by the Polypes, and united into a regular structure. Myriads of architects are at work day and night, month after month, and we see their soft and gelatinous bodies, through the agency of the vital laws, conquering the great mechanical power of the waves of an ocean which neither the art of man nor the inanimate works of Nature could successfully resist."

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When we consider that these busy millions are silently laying the foundations of islands and of continents, the future abodes of man, we must feel that the poet did not overestimate their importance when he termed them,

"Unconscious, not unworthy instruments,
By which a hand invisible was rearing
A new creation in the secret deep."

ORDER IV.-SEA-MATS.-PLUMED POLYPES.

THE Polypes of the present order are of a higher grade than those we have been considering, and in structure approach to some of the soft-bodied animals or Mollusca. Each Polype is a distinct and perfect animal, and they do not exist as solitary individuals, but as populous communities. Their habitations or polypidoms, the little cities of which they are both the architects and the occupants, are very variable both

Fig. 14.-a, natural size.-b, a group in various positions, magnified.

in form and material, sometimes enamelling with delicate network the leaf of a sea-weed or the outside of a shell, at others rising into the aspect of miniature plants, or broad leaf-like expansions. Round the mouth is a circle of tentacula or claspers (Fig. 14), which can be extended or withdrawn at the pleasure of the animal. The tentacula are covered with minute hairlike bodies (cilia), which by their movements effect a double purpose, for they not only create currents which bring their food within the reach of the polypes, but they act, like gills, as organs of respiration.

To this class of Zoophytes belong the "Sea-mats;" or, to use a more scientific term, the species of the genus "flustra," a word derived from the Saxon, and signifying to weave. Some of these form a delicate gauze-like encrustation on shells and sca-weed; others present a leaf-like appearance of a determinate pattern, and furnish another example of the great abundance of animal life in some of the lower tribes. Though not thicker than common letterpaper, they exhibit, either on one or on both sides, successive rows of cells, each of which has been occupied by its own inhabitant. In one species found on these coasts, and with cells upon one side only, Dr. Grant calculates there are more than 18,000 Polypes; and the Rev. David Landsborough, in speaking of another, remarks, "by counting the cells on a square inch, I calculated that this web of silvery lace had been the work and habitation of about two millions of industrious, and, we doubt not, happy inmates; so that

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