35^ 



impartially and logically considered with reference to the points at 

 issue, and Mr. Owen stated that, having studied this collection with 

 much care, he should, in the first place, restrict himself to such 

 observations and arguments as would naturally flow -from an exa- 

 mination of the specimens themselves, apart from any history or 

 statement with which they had been accompanied when first placed 

 in his hands by Madame Power. 



The collection of Argonauts, — Cephalopods and shells, — preser\-ed 

 in spirits, included twenty specimens, at difl'erent periods of growth, 

 the smallest having a shell weighing not more than one grain and 

 a half, the remainder increasing, by small gradations, to the com- 

 mon-sized mature individual. 



Mr. Owen's first attention was dii'ected to the relative position of 

 the Cephalopod to its shell. In every case it corresponded to that 

 which obtains in the Pearly Nautilus, the siphon and ventral surface 

 of the Cephalopod being placed next the broad keel forming the ex- 

 ternal wall of the shell, the dorsal surface of the body next the invo- 

 luted spire or internal wall. In most of these specimens the velated 

 arms, which are nearest the involuted spire, were retracted ; but in 

 some of the larger examples they had been admirably preserved 

 in a fully-expanded and flexible state, and in their natural position 

 as envelopes of the shell. 



A second fact, of considerable weight in the debated point of the 

 parasitism of the Argonaut, was afforded liy this collection, viz. that 

 in ten of the younger specimens there were no ova in the shell, but 

 the body of the Cephalopod occupied the ivhole of the cavity of the 

 shell, to ujhich it accurately corresponded in form. It was scarcely 

 possible, Mr. Owen observed, to contemplate these specimens with- 

 out deriving a conviction that the body had served as the mould 

 upon which the shelly matter had been deposited ; and with re- 

 ference to the expanded membranes of the dorsal arms, to which 

 the office of calcification was assigned by Madame Power and M. 

 Rang, these, it should be remembered, were, in fact, essentially pro- 

 ductions of the mantle and possessed the same structure. It was 

 only in the smaller specimens, however, that the body filled the 

 shell ; when the ovarium begins to enlarge, the body is drawn from 

 the apex of the shell, and the deserted place is occupied chiefly by 

 the mucous secretion of the animal until the ova are deposited 

 therein. 



Mr. Owen then reminded the members present, that in former 

 discussions on the nature of the Argonaut, he had opposed to the para- 

 sitic theory an observation made by himself on a series of young Argo- 

 nauts, of a different species from the Arg. Argo, all captured at the 

 same time, and exhibiting different sizes and degrees of growth, 

 viz. the exact correspondence between the size of the shells and t^t of 

 their inhabitants, every trijiing difference in the bulk of the latter being 

 accompanied with proportional differences in the size of the shells 

 which they occupied*. Madame Power's collection of young Argo- 

 nauts afforded the means of pursuing this comparison to a much 

 * Zool, Trans., ii. pt. ii. p. 115. 



