[522] English edition, p. 537, 1900. The chapter is revised by Prof. Alpheus Hyatt, to whom the nomenclature is largely due. For a more copious terminology, see Hyatt, Phylogeny of an Acquired Characteristic, p. 422 seq., 1894.
[523] This latter conclusion is adopted by Willey, Zoological Results, p. 747, 1902.
[524] See Moseley, op. cit. pp. 361 seq.
[525] In Nautilus, the “hood” has somewhat different dimensions in the two sexes, and these differences are impressed upon the shell, that is to say upon its “generating curve.” The latter constitutes a somewhat broader ellipse in the male than in the female. But this difference is not to be detected in the young; in other words, the form of the generating curve perceptibly alters with advancing age. Somewhat similar differences in the shells of Ammonites were long ago suspected, by D’Orbigny, to be due to sexual differences. (Cf. Willey, Natural Science, VI, p. 411, 1895; Zoological Results, p. 742, 1902.)
[526] Macalister, Alex., Observations on the Mode of Growth of Discoid and Turbinated Shells, P. R. S. XVIII, pp. 529–532, 1870.
[527] See figures in Arnold Lang’s Comparative Anatomy (English translation), II, p. 161, 1902.
[528] Kappers, C. U. A., Die Bildung künstlicher Molluskenschalen, Zeitschr. f. allg. Physiol. VII, p. 166, 1908.
[529] We need not assume a close relationship, nor indeed any more than such a one as permits us to compare the shell of a Nautilus with that of a Gastropod.
[530] Cf. Owen, “These shells [Nautilus and Ammonites] are revolutely spiral or coiled over the back of the animal, not involute like Spirula”: Palaeontology, 1861, p. 97; cf. Mem. on the Pearly Nautilus, 1832; also P.Z.S. 1878, p. 955.
[531] The case of Terebratula or of Gryphaea would be closely analogous, if the smaller valve were less closely connected and co-articulated with the larger.