SOME NEW AND RARE CEPHALOPODA. 115 



The most interesting circumstance to be noted in Mr. Bennett's Argonaut, is its di- 

 minutive size, in connection with the large mass of ova which it has formed, excluded 



Limaces to repair accidental breaches in their shell, and which also differs from the originally formed shell. 

 When, however, fractures occur near the margin of the shell, they are repaired by a substance identical with the 

 rest of the shell, as has been shown by Mr. Charlesworth *; but whether these reparations are due to the Ce- 

 phalopod, or to some yet unlinown MoUusk, can of course only be determined when the question is decided 

 respecting the real constructor of the Argonaut. 



The true use and disposition of the palmated arms of the Ocythoe have been determined and described by 

 M. Sander Rang. The base of each of these arms passes out of the shell at the angle between the summit and 

 auricular process of the free margin, and the membrane expands upon the outside of the shell, and meets its 

 fellow at the flattened keel. These expansions are transparent in the living Argonaut, and are compared by 

 M. Rang to the thin lobes of the mantle which the living Cowry spreads over its shell. Thus, when the Argo- 

 naut creeps at the bottom of the sea, it carries the shell above it, supporting it by means of the palmated arms, 

 and moves along, its head being downwards, by means of the other three pairs of arms. M. Rang, who has 

 long devoted himself to the study of Malacologie, and who is allowed by M. De Blainville to be ' parfaitement 

 au courant de I'etat de la question,' derives from the preceding observations a conviction that the Ocythoe is the 

 true constructor of the Argonaut. M. De Blainville, however, sees in the palmated arms only the analogous 

 organs of the claspers at the extremity of the tail of the parasitic Paguri. 



I have frequently, however, seen Paguri, and especially young ones, in shells veiy disproportionate to their 

 own size ; but I have never observed an analogous disproportion between the Argonaut shell and its occupant. 

 In a series of six small Argonauts, Cephalopods and shells, captured at the same time in the South Pacific 

 Ocean, all individuals of the same species {Arg. rufa, O.), but all differing by slight gradations in size, and of 

 which five are young, and without ova, and totally fill the shell, there is an exact accordance between the size 

 of the shell and the size of the inhabitant ; a corresponding gradation of size is maintained in both. In a series 

 of several small and very young specimens of the Argonauta Argo, which I examined whilst they were tempo- 

 rarily deposited by Madame Power in the hands of Mr. Charlesworth, and which, from the shght difference 

 of size, must have exhibited stages of growth differing at most by a few days only, there was the same exact cor- 

 respondency between the size of the Cephalopod and that of its shell. Now to explain this accordance between 

 the Cephalopod and shell on the parasitic theory, we must have recourse to the supposition that the Argonauts 

 change their shell at very brief intervals : indeed the chief business of their lives would be in that case to hunt 

 out, seize, and dispossess the (assumed, but yet unseen) true constructor of the shell, in oi'der to present so con- 

 stant a harmony in the relative proportion of the Cephalopod and shell which my observations on two series of 

 two different species of Argonaut have shown to exist. 



On the same occasion that I compared together the interesting series of the young specimens of Argonauta 

 Argo, I examined the small vermicular bodies supposed by Madame Power to be the newly-excluded young of 

 the A. Argo ; these were, however, young specimens of the parasite of the Argonaut described by Cuvier under 

 the name of Hectocotylus, which in the disposition of its numerous suckers, offers a remarkable resemblance to 

 the arm of an acetabuliferous Cephalopod. 



I cannot help further observing that the apparent strength of the main argument for the parasitic nature of 

 the Ocythoe, is its real weakness, since it arises from a view of analogy contracted within the artificial limits of 

 the systematist. The argument runs thus : Because the Ocythoe has no muscular attachment to its shell, and 

 because it is said to leave it and return to it at will, and to have no fixed relative position (.') to the shell, and 

 because there is no other testaceous Mollusk in the same predicament, therefore the occupant of the Argonaut 

 shell is a parasite. But surely we are justified in extending our views of analogy in such a question beyond the 

 limits of an artificial group, and we have not to look very far into the animal series before we find, in the Ser- 



* Magazine of Natural History (New Series), 1S37, p. 526. 



