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Show 186/.] DR. J. E. GRAY ON SPONGES. 501 long cilia, supported by a skeleton consisting of calcareous or siliceous spicules or horny network, The spicules have a distinct animal basis; hence it seems probable that each spicule was originally a segment of sarcode which has undergone calcification or silicifica-tion, and by the self-shaping power of which the form of the spicule is mainly determined. The mass of sarcode and spicules called the Sponge is permeated by a series of canals having a distribution proper to each kind of sponge. The ciliated cells seem to form the walls of the canals, which may be said to commence in the small pores of the surface and to terminate in the large vents or oscules ; and a current of water is continually entering at the former and passing forth from the latter during the life of the sponge, bringing in alimentary particles and oxygen, and carrying out excrementitious matter (see Dr. Carpenter's ' Microscope,' p. 530). The sponges are reproduced or multiplied by gemmation, which is effected by the detachment of minute globular particles of sarcode (covered with a more or less distinct thin membranaceous skin) from the interior of the canals, when they sprout forth as little protuberances, whose foot-stalks gradually become narrower and narrower until they give way altogether. These gemmules, like the zoospores of Algae, possess cilia, and, issuing forth from the vent, transport themselves to distant localities, where they lay the foundation of new fabrics. According to the observations of Mr. Huxley on the marine genus Tethya (Ann. & Mag. N. H . vii. 1851, p. 370), a true sexual generation also takes place, both ova and sperm-cells being found imbedded in the substance of the sponge. The bodies distinguished as capsules (ovisacs), which are larger than the gemmules, and which usually have their investments strengthened with siliceous spicules very regularly disposed, are probably the product of this operation. They contain numerous globular particles of sarcode, every one of which when set free by the rupture of the envelope (?) becomes an independent amccba-like body, and may develope itself into a complete sponge. The phenomena of sexual reproduction and development have since been more particularly studied in the Spongillce or Freshwater Sponges, especially by Mr. Carter (Ann. & Mag. Nat. Hist. xiv. 1854, p. 334, & xx. 1857, p. 21), and by Lieberkuhn in Muller's 'Arch.' 1856, in ' Reichert und du Bois-Reymond's Arch.' 1859, abstracted in 'Ann. & Mag. Nat. Hist.' xviii. 1856, p. 403, and the 'Quarterly Journ. of Microscopic Science/ v. 1857, p. 212. From the observations of Mr. Carter (Ann. & Mag. Nat. Hist. iv. 1849, p. 81) the sponge appears to begin life a solitary amceba ; and it is only in the midst of an aggregation formed by the multiplication of these that the characteristic sponge-structure makes its appearance, the formation of the spicules being the first indication of such organization. In this essay I have made free use of the very accurate and admirable figures of the spicules in the plates that accompany Professor 0. Schmidt's and, especially, Dr. Bowerbank's works and papers, |