Elements of conchology Prepared Elements of conchology / Prepared for the use of schools and colleges elementsofconcho00rusc Year: 1844 CUTTLE-FISHES.—NAUTILUS. appendages arranged like the calmaries; but their body, which is oval and depressed, is furnished with fleshy, lateral fins, occu- pying the whole length of the sack, and the back is sustained by a large internal shell, the structure of which has been already mentioned. The species most commonly found in the seas of Europe—Sepia officinalis—attains a foot in length or more. The cuttle-fish bone or shell, in powder, is used as a denti
Elements of conchology Prepared Elements of conchology / Prepared for the use of schools and colleges elementsofconcho00rusc Year: 1844 CUTTLE-FISHES.—NAUTILUS. appendages arranged like the calmaries; but their body, which is oval and depressed, is furnished with fleshy, lateral fins, occu- pying the whole length of the sack, and the back is sustained by a large internal shell, the structure of which has been already mentioned. The species most commonly found in the seas of Europe—Sepia officinalis—attains a foot in length or more. The cuttle-fish bone or shell, in powder, is used as a dentifrice, and is employed in the arts for several purposes, as for polishing, for forming moulds for silver castings, and as a pounce. 24. The family of CErHALOPODA Tetrabranchiata has for i'ts type the Nautilus, a very remarkable mdllusk, the body of which is enclosed in the last chamber (a) of a large shell, folded • spirally, and divided by transverse partitions (b) into several cavities, (Jig. 15). Each one of these par- titions is pierced by a hole, and the canal thus formed, which is called the syphon (s), extends to the pos- terior extremity of the shell; it is traversed by a contractile mem- branous tube, posterior to the body of the animal. This structure seems designed to facilitate the as- cent or descent of the animal in the water, by increasing or diminishing the specific gravity of the shell ; for the syphon communicates with an external reservoir, and can empty or distend itself with the water found in it; now, the chambers which it passes through are filled with air, and when this tube becomes inflated, it must compress this elastic fluid, and increase its density, which, at the same time, augments the specific gravity of the whole shell, and must give it a tendency to sink towards the bottom of the water in which it floats. 25. The conformation of the animal differs very much from that of the poulpes, calmaries, and other dibranchial cephalopods. The head
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