Note 425 — Chapter IX · ON CONCRETIONS, SPICULES, AND SPICULAR SKELETONS
Reading edition
See for instance other excellent illustrations in Carpenter’s article “Shell,” in Todd’s Cyclopædia, vol. IV. pp. 550–571, 1847–49. According to Carpenter, the shells of the mollusca (and also of the crustacea) are “essentially composed of cells, consolidated by a deposit of carbonate of lime in their interior.” That is to say, Carpenter supposed that the spherulites, or calcospherites of Harting, were, to begin with, just so many living protoplasmic cells. Soon afterwards however, Huxley pointed out that the mode of formation, while at first sight “irresistibly suggesting a cellular structure, ... is in reality nothing of the kind,” but “is simply the result of the concretionary manner in which the calcareous matter is deposited”; ibid. art. “Tegumentary Organs,” vol. V, p. 487, 1859. Quekett (Lectures on Histology, vol. II, p. 393, 1854, and Q. J. M. S. XI, pp. 95–104, 1863) supported Carpenter; but Williamson (Histological Features in the Shells of the Crustacea, Q. J. M. S. VIII, pp. 35–47, 1860) amply confirmed Huxley’s view, which in the end Carpenter himself adopted (The Microscope, 1862, p. 604). A like controversy arose later in regard to corals. Mrs Gordon (M. M. Ogilvie) asserted that the coral was built up “of successive layers of calcified cells, which hang together at first by their cell-walls, and ultimately, as crystalline changes continue, form the individual laminae of the skeletal structures” (Phil. Trans. CLXXXVII, p. 102, 1896): whereas v. Koch had figured the coral as formed out of a mass of “Kalkconcremente” or “crystalline spheroids,” laid down outside the ectoderm, and precisely similar both in their early rounded and later polygonal stages (though von Koch was not aware of the fact) to the calcospherites of Harting (Entw. d. Kalkskelettes von Asteroides, Mitth. Zool. St. Neapel, III, pp. 284–290, pl. XX, 1882). Lastly Duerden shewed that external to, and apparently secreted by the ectoderm lies a homogeneous organic matrix or membrane, “in which the minute calcareous crystals forming the skeleton are laid down” (The Coral Siderastraea radians, etc., Carnegie Inst. Washington, 1904, p. 34). Cf. also M. M. Ogilvie-Gordon, Q. J. M. S. XLIX, p. 203, 1905, etc.