[74] Mr. Broderip supposes it to have had the power of swimming freely, and of seeking its future habitation, as a bivalve; but Lovèn had not then made known to us the embryogeny and metamorphosis of the Conchifera. It is much more probable that the case is as I have ventured to assume in the text.
[75] Bennett.
[76] Rumphius.
[77] The periodical formation of these septa in the progress of growth, is analogous to that of the projecting external plates in the Wendletrap, and of the rows of spines in the Murex; but those external processes consist of the opake calcareous layer of the shell, whilst the internal processes in the Nautilus consist of the nacreous layer, like the septa in the Turritella. Thus the embryo Nautilus at first inhabits a simple shell, like that of most univalve Mollusca, and manifests, according to the usual law, the general type at the early stage of its existence; although it soon begins, and apparently before having quitted the ovum, to take on the special form.—Prof. Owen's Lect. on Invertebrate Anim. p. 593, 2d Ed.
[78] Woodward's "Manual of the Mollusca," p. 83.
[79] Carpenter, on the Microscope, &c., p. 602.
[80] Grant's Comp. Anat., 53.
[81] See Jones's General Outline, p. 506. (Ed. 1841.)
[82] Such is the common statement. Dr. Harlan, however, observes that "the rattle is cast annually [with the sloughed skin], and, consequently, no inference as to the age of the animal can be drawn from the number of pieces which compose the rattles." (Journ. Acad. Nat. Sci.; v. 368.) I confess this appears to me to be a non sequitur; for is it not quite possible that one may be added to the number annually, without involving the actual perpetuity of the preceding ones? It is evident that the increase must take place at some time or other, and it seems to me more likely to occur at the sloughing of the skin, that is, annually, than either oftener or seldomer.
[83] Martin "On the Horse," p. 111.