428 l'KOF. OWEN ON THE ARGONAUT. 



which Madame Power and M. Sander Rang compare to the lohes of tlic 

 mantle of Cyprcea ; and that the cephalopod in question, instead of agree- 

 ing in structure with the naked cephalopods, differs from them precisely 

 in the presence of conspicuous and largely-developed organs, which present 

 the closest correspondence in form and structure with the calcifying mem- 

 branes of the cowries and other testaceous molluscs. 



"2ndly. Mr. Gray asserts, ' that the shell of the argonaut is evidently 

 not moulded on the body of the animal usually found in it, as other shells 

 are.' 



" This assertion, like the preceding, is directly opposed to the fact. But 

 at the time when it was recorded in our Proceedings, Mr. Gray had proba- 

 bly not examined the young argonaut. Yet the analogy of other Testacea 

 might have indicated to him that it was essential to see the young mollusc 

 before the degree of correspondence between the animal and its shell could 

 be definitively pronounced upon. Most shell-bearing gastropods, like the 

 nautilus and argonaut, withdraw their bodies in the progress of growth 

 from the contracted apex by which their shell commenced, and differ ac- 

 cordingly in form from that of the original cavity of their shell. The 

 mode in which the vacated part of the shell is dealt with in different mol- 

 luscs is extremely various, and reducible to no common law ; in the genus 

 Magilus, e. g. it is solidified : in some species of Helix, Bulinus, and Ceri- 

 thium, the deserted part of the shell, after being partitioned off, is decolla- 

 ted : in the Nautilus, &c, it is camerated. Was it at all improbable that 

 in the argonaut some other condition of the vacated spire of the shell should 

 be manifested ? Why should it not be made subservient to the generative 

 economy of the species ? Yet, because it is neither solidified, decollated, 

 nor camerated, it is argued in the third place, that the argonaut shell must 

 have been secreted by some other mollusc than the cephalopod usually 

 found in it. 



" 4thly. Mr. Gray observes, ■ the young shell of the j ust-hatched animal, 

 which forms the apex of the shell at all periods of its growth, is much larg- 

 er (ten times) than the eggs contained in the upper part of the cavity of 

 the argonaut.' The argument here founded on a comparison of the size 

 of the supposed nucleus of the argonaut-shell with that of the ovum of the 

 Ocyth'6e,h&s been quoted with approbation by M. de Blainville ; but grant- 

 ing that the shell of a testaceous mollusc is always formed before the em- 

 bryo is excluded from the ovum, (which, as I have already shown, is a 

 postulate, and not an established law) the force of an argument for the 

 parasitic theory, based on this postulate, wholly depends upon another as- 

 sumption, viz. that the ovum of a mollusc never enlarges after it has quit- 

 ted the parent. Now, the first observation which the promulgator of this 

 argument had the opportunity of making on one of our commonest littoral 

 Testacea — the whelk, proved to him that the molluscous ovum in that spe- 

 cies does enlarge after exclusion, and Mr. Gray was subsequently compelled 

 to admit ' that the size of the nucleus would not offer any difficulty with 

 respect to the Ocythoe being the maker of the shell which it inhabits. 1 ' 



" Whether the other arguments founded by Mr. Gray upon the form of 

 the body, and the want of perfect adaptation or adhesion of the body to the 

 shell, &c, are unanswerable, as that experienced Conchologist states that 

 he considers them to be, must depend upon the degree of weight which the 

 objections above advanced are allowed to carry. 



" With respect to the conclusions as to the parasitism of the Ocythoe, 

 drawn from observing the relation of the cephalopod to its shell, their in- 



1 Magazine of Natural History, New Scries, 1837, p. 248. 



