But this must be done satisfactorily, and with the requisite knowledge, care, and good faith on the part of the observer.
Before, however, quitting this subject, we will mention one example of a naked Ce phalopod, nearly allied to Ocythoe, having manifested a parasitic propensity similar to that which is laid to the charge of that genus. A medical gentleman, (Dr. Moffat, of the Hon. East India Company's Ship, Flora,) who had collected objects in Natural History in the East Indies, amongst other specimens brought home an Octopus, which was caught in the Madras roads in his presence, by means of a baited hook and line, and, when drawn out of the water, was found to have its ven tricose body firmly imbedded in a ghee-bowl, (one of the small round pots in which the fluid butteris brought on board ship,) which had been thrown overboard. The Doctor disengaged the Cephalopod from the bowl before placing it in spirits, and when we related to him the interest which the fact possessed in consequence of the problematic nature of the Argonaut shell, of which he was not before aware, he regretted much that he had not preserved the Octopus in the singular domicile which it had chosen. Another instance of the parasitic appropriation of a dwelling-place by a Poulp is related by M. Desjardins, in the Report of the Natural History Society of the Mauritius ; he found an Octopus Arenarius in the shell of a Dolium.
The parasitic occupation of shells by the Octopi for the purpose of depositing the ova in them was not unknown to Aristotle. KAI it7TOTIXTEG els it4EV 7rOMIVOUC Eic Tac aclattishac EIC XEptsfASOY 11 Ts xcao gfAcnov, &C. " And the Polypus oviposits in cavities or in shells, or some such hollow places."* To return to the shells of the Dibranchiate Cephalopoas ; these, then, with the doubtful exception of the Ocythoe, are always internal, and either camerated and siphoniferous, or laminated and more or less rudimental, and concealed within the substance of the mantle.
In Octopus and Eledone the traces exist in the form of two small amber-coloured styli form bodies, lodged loosely in capsules, (im bedded in the sides of the mantle,) and ex tending downwards from the insertion of the shell muscles, close to the base of the bran chim. When the capsules are laid open, the styles frequently fall out in pieces, being of a friable texture. In the Octopus the styles are straight and elliptical ; in Eledone they are largest at their upper extremities, and become filiform as they pass in a curved direction downwards.
In all the Decapoda in which the shell is rudimental, it is represented by a single piece lodged in the middle line of the dorsal region of the mantle. It is of a horny texture in all the genera except the Sepia, and has generally more or less the form of a feather, as in the Calamary (fig. 228), or of a straight three edged sword.
According. to Aristotle the hard dorsal body of the Cuttle-fish was called by the Greeks sepion,' that of 'the Calamaries xiphos.'* In Sepiola and Rossia the gladius does not reach half-way down the back, beginning at the anterior margin of the mantle, 3,vhich in the latter genus is free. In Loligopsis, Gran chia, 0 nycoteuthis and Loll go, it extends the whole length Of the posterior part of the mantle. In Sepioteuthis it rivals in breadth the Sepium or Cuttle-bone, but is horny and elastic, as in the Calamary. In the latter the gladius is multiplied by age, and several are found packed closely one behind another in old specimens.
The Sepium or Cuttle-bone (fig. 229) is a well-known substance, and formerly figured in the Materia Medica as an antacid. It is a light cellular calcareous body, of a peculiar form and structure ; and, as it is confined ex clusively to the genus Sepia, its presence alone serves to characterise that section of Cepha lopods. Its form is an elongated oval, de pressed, convex on the dorsal surface, partly convex and partly concave on the opposite side: it terminates posteriorly in a very thin, dilated, aliform margin (a, a), partly calca reous and partly horny, which becomes nar rower as it advances forwards, and is gradually lost in the sides of the shell. As this margin is inclined towards the ventral aspect, it pro duces at the posterior and ventral side of the shell a wide and shallow concavity, comparable to the chamber of the Nautilus shell 3,vhich protects the body of that species : if the free margin of the sepium were in like manner produced beyond the previously deposited layers, it would advance from the posterior and lateral aspects of the animal, and cover the ventral surface, as in the Nautilus, leaving the convexity produced by the chambered portion projecting into the back. The thickened part of the sepium (b) which retains that situation, is in fact composed of a series of thin parallel calcareous plates, successively deposited and extending obliquely forwards from the ventral to•the dorsal surface : the last formed plate is the most internal and the broadest, but not the longest also, as in the Nautilus ; its develop ment being limited to the anterior part of the shell, so that the previously deposited layers appear successively behind it forming irregular sinuous transverse striw (c). The intervals of the plates are occupied by crystalline fibres, passing perpendicularly from one layer to the other : A is a magnified view of this structure. At the posterior part of the sepium, a little anterior to the thin margin, a pointed booked process projects backwards : this differs in size and shape in different species of Sepia ; but it is always characteristic of the peculiar production which has been described, and has served to identify some doubtful fossils.