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, ãThese shells [Nautilus and Ammonites] are revolutely spiral or coiled over the back of the animal, not involute like Spirulaã: 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.
532 ãIt has been suggested, and I think in some quarters adopted as a dogma, that the formation of successive septa [in Nautilus] is correlated with the recurrence of reproductive periods. This is not the case, since, according to my observations, propagation only takes place after the last septum is formed;ã Willey, Zoological Results, p. 746, 1902.
533 Cf. Woodward, Henry, On the Structure of Camerated Shells, Pop. Sci. Rev. XI, pp. 113ã120, 1872.
534 See Willey, Contributions to the Natural History of the Pearly Nautilus, Zoological Results, etc. p. 749, 1902. Cf. also Bather, Shell-growth in Cephalopoda, Ann. Mag. N. H. (6), I, pp 298ã310, 1888; ibid. pp. 421ã427, and other papers by Blake, Riefstahl, etc. quoted therein.
535 It was this that led James Bernoulli, in imitation of Archimedes, to have the logarithmic spiral graven on his tomb, with the pious motto, Eadem mutata resurgam. On Goodsirãs grave the same symbol is reinscribed.
536 The ãlobesã and ãsaddlesã which arise in this manner, and on whose arrangement the modern clasôÙsiôÙfiôÙcaôÙtion of the nautiloid and ammonitoid shells largely depends, were first recognised and named by Leopold von Buch, Ann. Sci. Nat. XXVII, XXVIII, 1829.
537 Blake has remarked upon the fact (op. cit. p. 248) that in some Cyrtocerata we may have a curved shell in which the ornaments apôÙproxôÙiôÙmateôÙly run at a constant angular distance from the pole, while the septa apôÙproxôÙiôÙmate to a radial direction; and that ãthus one law of growth is illustrated by the inside, and another by the outside.ã In this there is nothing at which we need wonder. It is merely a case where the generating curve is set very obliquely to the axis of the shell; but where the septa, which have no necessary relation to the mouth of the shell, take their places, as usual, at a certain definite angle to the walls of the tube. This relation of the septa to the walls of the tube arises after the tube itself is fully formed, and the obliquity of growth of the open end of the tube has no relation to the matter.