Spirals in Nature and Art; A Study of Spiral Formations Based on the Manuscripts of Leonardo Da Vinci, with Special Reference to the Architecture of the Open Staircase at Blois, in Touraine, Now for the First Time Shown to Be from His

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1903 edition. Excerpt: ...dextral as an adult. If we take the Telescopium shown in fig. 27 as an example of a conical spiral, the Nautilus pompilius in fig. 34 will be a good instance of the flat spiral, in which all the whorls are practically in one plane. In this picture, the little projection noticeable in each compartment of the shell is the siphuncle, a membranous tube perforating the septa, which Owen thought was connected with the pericardium, and which may serve to lighten the shell by the passage of some gas into its various chambers. In the Nautilus it nearly always projects backwards, but in the Ammonites it nearly always projects forwards. Among the Stephanoceratidae, Crioceras bifurcatum has disconnected whorls, as if the various coils of an Ammonite had not joined together, and it looks something like a ram's horn, or a rather complicated hook. Oncyloceras spinigerum is a fossil tetrabranchiate cephalopod, in which the whorls are also disconnected. Siliquaria anguina has a shell that begins in a close spiral and ends in irregular separated coils. Cylindrella, the cylinder-snail of the West India islands, a palmonate gastropod of spiral form, has the last whorl detached from the rest, with a circular mouth-opening. In the British Museum of South Kensington, there are very fine examples of Macroscaphites gigas, and Macroscaphites ivanii, which look like Ammonites beginning to unroll themselves; and if the logarithmic curve in fig. 35 be taken as the expression of "uniform growth" in all organic matter, as Mr Church suggests it may be used in plant-protoplasm, it may be conceived as possible that as the surviving Nautilus (fig. 34) differs from it in taking a wider sweep, while the fossil Ammonite differs in exhibiting a tighter spiral, so the...