two lakes of equal dimensions.

Sometimes the whole

bladder wrinkles and partially collapses into a rugose column, and then slowly distends again, when the openings are seen as they were before.

"The efferent stream pours out at each of these orifices, carrying with it fœcal matters from the interior, and any light-floating atoms that may be in the vicinity, as I saw with beautiful distinctness, by making the surrounding water slightly turbid.

"On my touching the bladder with the point of a needle, it at once shrank up into a wrinkled column, but did not retract, and presently distended again. Thus the specimen exhibited very distinctly those characteristics of animal life -sensibility to touch, and spontaneous movements."

* Tenby, 320.

CHAPTER IV.

PORIFERA (Sponges).

Continued.

THOUGH the horny or keratose Sponges are distinguished from those which have calcareous or siliceous spicula in them, this distinction must not be understood to imply that the former are totally destitute of these bodies, but only that they possess them in an excessively minute proportion. Mr Bowerbank, in his elaborate and valuable investigations "On the Keratose Sponges of Commerce," has found spicula of very minute dimensions imbedded in the substance of the horny fibres of various species. Still the immense preponderance of the corneous structure fully warrants their isolation as a natural group.

The horny fibres, as we have already said, form an irregularly netted mass, uniting to and separating from each other at various angles and distances, without the least order. They are not tubular, as has been supposed, but solid and of unequal thickness in different parts. Sometimes they are rigid and coarse, as we have seen in a large tubular Sponge on the shores of Jamaica, almost

* Trans. Micr. Soc. i., p. 32.

emulating the entangled twigs of a thorny bush in their inelastic stiffness. But more commonly the slenderness and arrangement of the fibres impart to the Sponge that elasticity which is one of its most valuable qualities.

In order to apprehend truly the character of any Sponge, it should be examined alive if possible; but if this be impracticable, at least specimens should be selected which have been dried as they came from the sea, without having been subjected to any processes of washing, pressing, or cleansing. In specimens of Turkey Sponge in this condition, Mr Bowerbank finds the horny fibres surrounded by a beautiful tissue of branching vessels in great abundance, enclosed in an external membrane or sheath. This tissue Mr Busk has succeeded in injecting with coloured fluid.

The fibres are also covered with a web of darker colour than their substance, composed of minute granules, which are conjectured to be incipient gemmules; for nucleated gemmules were found on the fibres of other specimens, in which the granulose texture was wanting. The maceration in fresh water, however, and the immersions in diluted acid to which the commercial Sponges are subjected, remove the whole of the gelatinous flesh, and render this structure inapparent in specimens sold in the shops.

In commerce two kinds of Sponge are known-the Turkey and the West Indian. But of the former Mr Bowerbank makes two species, undistinguishable indeed by any marks that the naked eye can appreciate, but recognised in an instant on microscopical examination, by the presence or absence of the investing vascular tissue above men

tioned. Both of these species grow abundantly in the eastern parts of the Mediterranean, especially around the numberless islets of the Grecian Archipelago. Smyrna is the great market for the Sponge trade, and the exportation of this article forms no inconsiderable source of its prosperity.

Great Britain imports annually about 60,000 lbs. of Sponge, paying duty of 6d. per lb., with five per cent. addition. The greater portion comes from the Levant, but Barbadoes and the Bahamas supply a coarser sort, chiefly used for washing carriages. Its pores are large, and it has projecting lobes; the fibres possess little cohesion, and hence it is commonly called "rotten."

The Grecian Sponges grow in moderately deep water, usually assuming a more or less manifest cup-form. Those which reside in the deeper recesses of the sea are said to be of larger dimensions, as well as of finer texture, than such as are more exposed to the action of the waves. Aristotle, who enjoyed peculiar facilities for the study of these organisms, and who has speculated on their nature, says that in a living state they are black, except as covered with the light earthy sediment of the sea :—a circumstance which, notwithstanding his high authority, we venture to doubt. He may possibly have supposed specimens to be alive which were dead, and blackened with sulphuretted hydrogen.

In many of the Greek islands, the diving for Sponge forms a considerable part of the occupation of the inhabitants, as it has done from the most remote antiquity. Hasselquist says:-"Himia is a little, and almost unknown island directly opposite Rhodes. It is worth notice, on

account of the singular method the Greeks, inhabitants of the island, have to get their living. In the bottom of the sea the common Sponge is found in abundance, and more than in any other place in the Mediterranean. The inhabitants make it a trade to fish up this Sponge, by which they get a living far from contemptible, as their goods are always wanted by the Turks, who use an incredible number of Sponges at their bathings and washings. A girl in this island is not permitted by her relations to marry before she has brought up a certain quantity of Sponges, and before she can give a proof of her agility by taking them from a certain depth." In other islands the same custom prevails, but with reversed application, as in Nicarus, where the father of a marriageable daughter bestows her on the best diver among her suitors,—“He that can stay longest in the water, and gather the most Sponges, marries the maid." †

"

In fact, the employment seems to be common to both sexes and all ages. Savary, describing a little insular dependence of Rhodes, named Syme, observes as follows:— "The Sponges which grow around this isle are the only resource of the inhabitants. Men, women, and children, all learn to dive. All must seek beneath the waters the only patrimony which nature has left them. The men excel all in this dangerous art. They precipitate themselves into the sea, and descend to an enormous depth. Often they do violence to themselves in retaining their breath too long, and on emerging vomit a mouthful of blood. At other times they run the risk of being devoured

*Voyages in the Levant (1766), 175.

+ Pomet's Hist. of Drugs, v. 102.