Besides the colouring matter, another kind of product is secreted between the corium and cuticle, viz. the shell : this presents diffe rent degrees of development in different genera. M. De Blainville in France, and Leach, Broderip, Gray, and Sowerby, among the able naturalists of our own country, maintain that the Argonaut shell is not the product of a Cephalopod, but of some inferior Mollusk, allied to the Carinarim, whose shell Linnceus indeed placed in the same genus with the Argonauta, in consequence of the close rela tionship subsisting between them, both in form and structure. The principal grounds for this 'opinion are the following. The Ocythoe has no muscular or other attachment to the Argo naut shell. When captured, and placed alive in a vessel of sea-water, it has been seen vo luntarily to quit the shell, and in one instance without manifesting any disposition to return to it. In this state, viz. without its shell, it was described by Itafinesque as a new genus of Cephalopod under the name of Ocytha, and De Blainville who first recognized this genus as being founded on an animal identical with the Cephalopod of the Argonaut, or the Nautilus przmus of the ancients, retained the name in order to distinguish the supposed parasite from the shell which it had, according to this theory, adopted. Agreeably with the absence of any natural connexion between the Ocythoe and the shell in question, is the fact that this animal is not found in any constant or regular position in the shell. In most examples we have found the funnel and ventml aspect of the body turned towards the external wall of the shell, as in the figure (jig. 206). The Cranchian speci men figured by Mr. Sowerby was in the same position. In the specimen which M. De Blain ville* has carefully delineated for this pur pose, the back of the Ocythoe is next the invo luted convexity of the shell, the funnel is towards the opposite expanded concavity, but turned out of the middle line, and separated from the parietes of the shell by the retracted feet. In the figure which illustrates Brode rip's excellent Mernoir,i- the animal is repre sented with the funnel next the involuted crest of the shell. In another specimen in the unique collection of the same Naturalist, the Cephalo pod is retmcted on a mass of ova, its arms hud dled together, and its funnel projecting from the middle of one side of the shell; on the op posite side numerous suckers are seen expand ed and applied to the inner surface of the shell, demonstrative of the abnormal mode of its ad hesion to that body.
Whatever be the position in which the Ocythoe is found, the whole of the exterior surface of its mantle is coloured as in the naked Cephalopods, which seems to indicate that it has not been permanently excluded from light by an opake calcareous covering, such as the Argonauta shell must have formed if it had been applied to the body of the Ocythoe ab ova. What is, more remarkable, and con trary to the analogy of true testacea; is, that there is little or no correspondence between the disposition of the colour of the Ocythoe and that of the Argonaut shell. The external sur face of the skin ot the Ocythoe has the same entire epidermic covering as in the naked Poulp, yet the Argonaut shell is furnished with a delicate epidermis in its natural state.
All Mollusks which are naturally pro vided with external shells have them for pro tecting either a part or the whole of the body ; and in the latter case the interior of the shell is always kept clear, that the animal may retire to it for safety; but this retraction into the hol low of the shell is impossible to the Ocythoe, at least in those numerous cases in which the shell is found more or less filled 'with masses of ova. Other Cephalopods, with external shells, indubitably their own, as the Pearly Nautilus, have adequate muscular attachments ; and it may reasonably be asked does the Argo naut afford a valid exception to this rule ? Such an exception indeed it must form if the shell be really secreted, as the Continuator of Poli asserts, by the Cephalopod inhabi tant ; and not only in this particular, but in every principle which has been established in reference to the relations of a shell to the body and the reciprocal influences affecting them in the Molluscous classes.
The naturalists who maintain that the Ce phalopod of the Argonaut and the shell are parts of one and the same animal, insist on this unde niable fact, that from the time of Aristotle to the present day the Argonaut shell has never been found with any other inhabitant than the Ocythoe ; and, -what is of more weight, that the Ocythoe has never been found in any other shell than the Argonauta. Whereas the Hermit-Crab adopts different species as they happen to fall.in his way. And further, that the different species of Argonauta, as the A. Argo, A. tuberculata, and A.hians, have each different species of Ocy tha. We may add that the light fragile tex ture of the Argonauta shell, like that of Ca rinaria, bespeaks a floating oceanic species, and not a Mollusk that creeps at the bottom, and therefore the probability is less that its real inhabitant should have escaped the notice of the Naturalist, supposing the Cephalopod to be a parasite.
In the posthumous volume of Poli's great work on the Sicilian Testacea, it is stated that that naturalist watched the daily development of the ova of an Ocythoe contained in an Ar gonaut shell, and that, by means of the micro scope, he detected the rudiment of the shell in the embryo : the completion of the experi ment was, however, accidentally interrupted ; and the figure which the editor Della Chiaje has published of the ovum, which it was hoped would have determined the question, seems to shew the yolk appended to the embryo instead of the shell.
Mr. Gray,* on the other hand, has recently stated that the nucleus of the Argonaut shell, or that part which, from analogy, must have been formed in the egg, is too large to have been formed in the egg of the Ocythoe. The arguments drawn from the microscopical exa mination of the ova of the Ocytho6 before the commencement of the development of the embryo, are obviously inconclusive; since, whatever the subsequent products of the egg might be, at this period only the granular and oily particles of the vitelline nidus could be expected to be seen.
With respect to another argument against the legitimate title of the Ocythoe to the shell, founded on the supposed uniform occurrence of a deposition of eggs in the same shell, vve can adduce three exceptions in which the Argonaut shell was exclusively occupied by the Cephalopod ; these specimens were taken along with several others, by Captain P. P. King, R.N., from the stomach of a Dolphin, caught upwards of six hundred leagues from land, and were kindly presented to us by that gentleman. In these examples, as in others, we were struck with the exact correspondence between the size of the shells and that of their inhabitants, every trifling difference in the bulk of the latter being accompanied with proportional differences in the shells which they occupied. The consideration of all these circumstances has prevented a satisfactory con clusion being formed with respect to this long agitated and nicely-balanced question, and we are compelled to repeat after the Stagyrite, irEpC ti xal 7,91; cbcpsf3c7); ithiv oi,wce clwrat.t Observation of the development of the Ocythoe until the period when it is cluded from the egg-, would decide the point.