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Show 970 PROF. OWEN ON THE [Nov. 19, For the different views which have been propounded as to the nature and function of this complex siphon, reference may be made to the authors cited, p. 966. Some of these views were based on the partial knowledge of its structure at the date of the first dissection of the Pearly Nautilus. The true structure of the siphon in Nautilus pompilius is rarely preserved; the somewhat loose calcareous matter by which the membranous part is incrusted is commonly lost with that part in the dry cast-off shells. The calcareous incrustation is apt to be dissolved, like that of the mandibles in Valenciennes's specimen, by the acetous change of the alcohol when charged with soluble parts of the animal during a prolonged transit to a European museum. Fig. 3. Nautilus striatus. Section of part of shell. When cataloguing, in 1854 and 1855, the Hunterian Cephalopods, I saw sufficient to supplement the description of the siphon in the ' Memoir on the Nautilus,' as follows : - " An artery and vein are assigned for its life and nutrition, and to extend a low degree of the same influences to the shell; but the structure of the membranous siphuncle presents, beyond the first chamber, an inextensible and almost friable texture, apparently unsusceptible of dilatation and contraction ; it is also coated beyond the extremity of the short testaceous siphuncle with a thin calcareous deposit"1. The fact of this incrustation has been ascertained, independently, by Prof. Vrolik. The subject of his memoir in the volume cited in note I, was 1 Descriptive Catalogue of the Fossil Organic Remains of the Invertebrata contained in the Museum of the Royal College of Surgeons of England, 4to, 1856, p. 29. This volume was not issued until all the invertebrate fossils were described ; and the first sheets were printed off before the ' M6moires de la Societe Linneenne de Normandie,' vol. x. 1855, came to m y hands. |