The propagation of the sponges is provided for in a no less wonderful manner than their respiration and nourishment. Minute globular particles of sarcode sprout forth as little protuberances from the interior of the canals. As they increase in size, they are gradually clothed with vibratile cilia, and, finally detaching themselves, are cast out through the oscula into the world of waters. Here their wanderings continue for a short time, until, if they be not devoured on the way, they reach some rock or submarine body on which, tired of their brief erratic existence, they fix themselves for ever, and, bidding adieu to all further rambles, lead henceforth the quiet sedentary life of their parents. In this manner the sponges, which otherwise would have been confined to narrow limits, spread like a living carpet over the bottom of the seas, and in spite of their being utterly defenceless, maintain their existence from age to age. At the same time they serve to feed a vast number of other marine animals, for the waters frequently swarm with their eggs, and these afford many a welcome repast to myriads of sessile molluscs, annelides, polyps, and other creatures small or abstemious enough to be satisfied with feasting on atoms. Sponges inhabit every sea and shore, and differ very much in habit of growth. For whilst some can only be obtained by dredging at considerable depths, others live near the surface, and others, again, attach themselves to the surfaces of rocks and shells between the tide marks. Like the corals, they revel in every variety of shape and tint, imitate like them every form of vegetation, and adorn like them the submarine grounds with their fantastic shrubberies. The fine collection of West Indian sponges exhibited in the Crystal Palace, but to which fancy must add the additional ornament of colour, may serve to give some idea of their prodigal versatility of growth. More than sixty different species have been discovered in the British waters alone, and as they go on increasing in numbers, size, and beauty, until they attain their highest development along the shores of the tropical ocean, they no doubt hold a conspicuous rank among the living wonders of the sea. The branched sponges, with a compact feltred tissue, are more common than others in the colder maritime domains, where the species of a loose texture, which grow in large massive forms, either do not exist or are very rare. Many sponges are of considerable size, such as the vase-like tropical species known under the name of Neptune's cup; others are almost microscopical; and while by far the greater number grow superficially from a solid base, some penetrate like destructive parasites into the texture of other animals. Thus the _Halichondria celata_ establishes itself in the small holes which some of the smaller annelides drill in the shell of the oyster, eat further and further into the unfortunate mollusc's vitals,