. Elements of zoology, or, Natural history of animals / ed. by Reese. Zoology. CLASS P0R1FERA THE SPONGES. 527 of a sort of network of filaments, interlacing together in such a manner as to leave large channels and spaces of various forms, which communicate with each other. The large channels ter- minate in the vents ; and, on tracing any one of them into the. External surface and sectional view of Living Sponge. substance of the sponge, it is seen to divide and send off rami- fying branches, which at last lose themselves in the spongy net- work that lies around them; and this communicate
. Elements of zoology, or, Natural history of animals / ed. by Reese. Zoology. CLASS P0R1FERA THE SPONGES. 527 of a sort of network of filaments, interlacing together in such a manner as to leave large channels and spaces of various forms, which communicate with each other. The large channels ter- minate in the vents ; and, on tracing any one of them into the. External surface and sectional view of Living Sponge. substance of the sponge, it is seen to divide and send off rami- fying branches, which at last lose themselves in the spongy net- work that lies around them; and this communicates with the pores on the external surface. 947. The interlacing fibres, of which the walls of the large canals, and the spongy tissue between them, are alike composed, entirely consist (in the common sponge) of a sort of horny ani- mal matter, as is shown by burning a small portion of them. But in other species we find tpicula, or needle-like crystals, of silex or of carbonate of lime, disposed amongst these, giving to the structure much greater firmness, but depriving it, more or less completely, of that elasticity which is so useful in the com- mon sponge. 948. The substance known as sponge is, however, but the skeleton of the being; when alive, this fibrous network is clothed, within and without, by a thin gelatinous substance, very like the white of an egg. This lines all the passages, and covers the exterior; but it drains away when the sponge is removed from the water. In this the peculiar vital endowments of the being appear to reside. These are manifested, not only by its slow but regular growth, but by a curious circulation of fluid, constantly taking place within the mass. When a sponge 972. Why are they included among animals ? 973. What structure is seen in the diagram ? 974. Describe the living Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illus
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