544 



CEPHALOPODA. 



of repose, and the vesicles are contracted and 

 invisible, the skin be slightly touched, the co- 

 loured vesicles show themselves, and in an in- 

 stant, or sometimes with a more gradual mo- 

 tion, the colour will be accumulated like a 

 cloud or a blush upon the irritated surface. If 

 a portion of the skin be removed from the 

 body and immersed in sea-water, the lively 

 contractions of the vesicles continue ; when 

 viewed in this state under the microscope by 

 means of transmitted light, the edges of the 

 vesicles are seen to be well denned, and to pass 

 in their dilatations and contractions over or 

 under one another. If the separated portion of 

 integument be placed in the dark, and exa- 

 mined after a lapse of ten or fifteen minutes, 

 all motion has ceased; but the vesicles, when 

 re-exposed to a moderately strong light, soon, in 

 obedience to that stimulus, recommence their 

 motions. As the vibratile microscopic cilia 

 have been recently traced through the higher 

 classes of the animal kingdom, it is not an un- 

 reasonable conjecture that equally inexplicable 

 motions of the colouring parts of the integu- 

 ment may also be detected in other classes 

 than that in which we have just described them, 

 and thus a clue may be obtained towards the 

 explanation of the influence of geographical 

 position on the prevailing colours of the animal 

 kingdom. 



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 Carinarire, whose shell Linnieus 

 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. \Vhencaptured, 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 Ilafinesque as a new genus 

 of Cephalopod under the name of Ocythoe, 

 and De Blainville, who first recognized this 

 genus as being founded on an animal identical 

 with the Cephalopod of the Argonaut, or the 

 Nautilus primus of the ancients, retained the 

 name in orderto 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 ventral aspect of the 

 body turned towards the external wall of the shell, 

 as in the figure (fig- 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 Memoir,t 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 retracted 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 

 ub ovo. 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 of 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 Poll 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 



Zoological Journal, vo 



p.l, 



ll. IV. 



