through the living mass, the sarcode obtains its nourishment, and the skeleton its growth by a sort of absorption, or what is known to the physiologist as endosmotic action of the cells. We have then mentioned above three clearly specialized functions, as represented respectively by the inhalant pores, the exhalant oscula, and the uniciliated cells. And it is certainly a matter of prime importance that each cell should have this single lash. In fact, it raises it to the rank of a pacha with one tail, in a community where all are pachas of this dignity, and each one a commissioner of the water department, and a commissary of subsistence. "Both the oscula and pores can be closed at the will of the animal; but the oscula are permanent apertures; whereas, the pores are not constant, but can be formed afresh whenever and wherever required."
The sponges are the active eliminators of the salts of the ocean. In a large laboratory certain substances are kept in solution, so as to be ready to the chemist's hands. Nature's grand laboratory is the sea. There her little economic chemists are ceaselessly busy extracting, and putting into solid forms, the various mineral substances held in solution. Thus the coral polyps eliminate the carbonate of lime with which to build their beautiful structures. And the Alcyonarian polyp in this way builds up the delicate sea-fan, with its skeleton of keratose, or horn-like substance. And so is it with the sponges. They, too, are elaborators of the mineral treasures of the sea. Hence it has been attempted to group them upon considerations of their special building propensities. In this way the toilet-sponges, and, in general, those of commerce, which all affect horn, or keratose, in the structure of their skeletons, would be grouped together as the Keratosa; while those which choose lime would be called Calcarea; and those which build up with silex would be known as the Silicea. We have mentioned these groups in their order of rank. The highest is the vitreous, or glass-sponge, with which we are directly concerned.
In the recent deep-sea dredging, so charmingly described in Dr. Wyville Thompson's new book, "The Depths of the Sea," an account is given of the obtaining in British waters, at the depth of 30,000 feet(!), specimens of the Hyalonema, the famous Glass-Rope Sponge. It had been previously obtained from the coasts of Portugal, when the news astonished naturalists, as previously it had only been known as coming from Japan. It is, indeed, a wonderful object. We once saw a specimen in the cabinet of a learned institution. The professor pronounced it a coil of Japanese spun glass. "No," said another savant, "it is a plant." And at that time both were excusable, for even Ehrenberg had looked upon it as "an artificial product of Japanese industry." That is to say, the great microscopist regarded the object as an ingenious imposition, consisting of natural products artfully put together. Let the reader carefully inspect the cut of Hyalonema, Fig. 1, which we have taken from Dr. Thompson's book, and then let us attempt a description.
