Fine sponges are used by physicians in surgical operations, and are sometimes very expensive. Should you at any time take a fancy to a dainty little sponge in the druggist's window, and step in, thinking to buy it, you will probably be surprised at the price asked for it. Our finest sponges come from the Mediterranean Sea and the Red Sea. They are obtained by divers, who search for them under rocks and cliffs, and who remove them carefully with a knife, that they may not be injured; The Turks, who carry on the trade, have between four and five thousand men employed in collecting sponges. The value of the sponges annually collected is estimated at ninety thousand dollars. Coarse varieties are found in the Gulf of Mexico and the Bahama Islands. They are scraped off the rocks with forked instruments, and consequently they are often torn.
The demand for sponges has increased so much during the last few years that there is cause to fear the supply will be exhausted, unless some way can be found to cultivate them by artificial means. With this view, attempts have recently been made to raise sponges in the Adriatic Sea by taking cuttings from full-grown ones, and fastening them upon stones on the bottom of the ocean until they attach themselves. These experiments have been successful, but the operation is a delicate one, requiring great care not to bruise the soft flesh. It is necessary to keep the sponge under sea-water during the process.
Fig. 3.—Glass Sponge.
Some of the glass sponges are exceedingly beautiful. The delicate "Venus's flower-basket" grows in the deep sea near the Philippine Islands. It looks like spun glass woven into a beautiful pattern, and is so exquisite we can scarcely believe that it is the skeleton of a sponge. Fig. 3 shows a remarkable specimen of the sponge family, taken between Gibraltar and the island of Madeira by the scientific party on board the famous Challenger, which ship was sent out for the express purpose of exploring the animal and vegetable wonders of the great deep.
This sponge, reduced in the illustration to one-third its size, is composed of bands of spicules running lengthwise from end to end, with cross bands at right angles. The corners are filled up with a pale brown corky-looking substance, reducing the spaces to little tube-like holes, and rising into spirally arranged ridges between them. The ridges, instead of having a continuous glassy skeleton, have their soft substance supported by a multitude of delicate six-rayed spicules interspersed with what under the microscope look like little stars and rosettes. The whole sponge is covered with fine hairs, and the mouth is closed by a net-work of a jelly-like substance supported by sheaves of fine needles. The glass-rope sponge roots itself in the mud by twisted fibres.
The boring sponge spreads itself over the shells of oysters and mussels, boring them through and through, and dissolving the shell. It even bores into solid marble, and will, in time, utterly destroy it.
Flints are exceedingly hard substances—so hard that when we wish to be emphatic, we sometimes say that a thing is as hard as flint. Yet all the flints in the world are supposed to have been formed from soft sponges. By examining small pieces of flint under a microscope the texture of the sponge, in a fossil condition, is often clearly seen, and the spicules peculiar to sponges are recognized.