In the months of April and May, these animalcules engender germs, round, yellow, or white, whence proceed certain ovoid granular embryos furnished towards their largest extremity with small vibratile cilia. They are thrown off by the currents, which serve as a stomach, and form swarms of larvæ round the polypier. They swim about with a gliding wavy motion, and when they have been some time in the water they usually come to the surface; but they are also often carried off by the current. During two or three days they seem to seek a convenient place to fix themselves. Once fixed, the larvæ loses the cilia, spreads itself out, and takes the form of a flattened gelatinous disk. Its interior organization consists of contractile cellules and numerous spiculæ--"a tribe," says Gosse, "of the most debateable forms of life, long denied a right to stand in the animal ranks at all, and even still admitted there doubtingly and grudgingly by some excellent naturalists. Yet such they certainly are, established beyond reasonable controversy as true and proper examples of animal life." It may, then, be safely asserted that all naturalists are now satisfied of the animal nature of sponges, although they represent the lowest and most obscure grade of animal existence, and that so close to the confines of the vegetable world, that it is difficult in some species to determine whether they are on the one side or the other. "Several of them, however," says Mr. Gosse, "if viewed with a lens under water while in a living state, display vigorous currents constantly pouring forth from certain orifices; and we necessarily infer that the water thus ejected must be constantly taken in through some other channel. On tearing the mass open, we see that the whole substance is perforated in all directions by irregular canals, leading into each other, of which some are slender, and communicate with the surface by minute but numerous pores, and others are wide, and open by ample orifices; through the former the water is admitted, through the latter it is ejected." It is not to be denied, however, that these beings constitute, in spite of investigations of modern naturalists, a group still somewhat problematical, and still very imperfectly known as regards their internal organization. Sponges are masses of a light elastic tissue, which is, at the same time, resistant, full of air-cells, and with much varied exterior arrangements. Nearly three hundred species are known, the different appearances of which have been characterised by names more or less singular. There is, for instance, the Feather Sponge, the Fan Sponge, the Bell, the Lyre, the Trumpet, the Distaff, the Peacock Tail, and Neptune's Glove. There are river sponges and sea sponges.