ON THE ARGONAUT. V 



and diaphanous nature of the shell, its sides, which so well 

 indicate the different applications of the anterior margin of 

 the membrane, its tubercles along the keel, constant in all the 

 species ; the coloration of the bases of the arms, correspond- 

 ing so well with the colouring of the keel towards the spire ; 

 — are not these characters, which, more thoroughly investi- 

 gated than they have yet been, would tend to support the 

 fact of the membranous arms being the organs of secretion ? 

 We shall be told that it is not by the aid of their mantle that 

 the Mollusca secrete their shells, but by the collar which 

 unites them to the opening ; and without doubt this is an 

 opinion very justly adopted, and we have proved by more 

 than one circumstance, and even in the preceding note, that 

 we have for a long time ranged ourselves on the side of this 

 opinion ; but the argument does not, for that reason, appear 

 to us the less feeble, for admitting it to be proved that it is by 

 the collar that the Mollusca secrete their shells, it is also 

 proved that there are exceptions to this nile. The mollusc 

 of the Nautilus, for example, the shell of which is very solid 

 and strong, and must have required two or three kinds of se- 

 cretion, has no collar, as a skilful English naturalist teaches 

 us by the anatomical examination which he has lately 

 made, and in which we find no mention of these organs. — 

 Now if the mollusc of the nautilus, without the aid of a col- 

 lar, has constructed a shell so strong, so heavy, and so emi- 

 nently calcareous, surely we may believe that the mollusc of 

 the argonaut, likewise a cephalopod, is equally capable of 

 constructing a shell without such aid. Such a supposition, 

 according to our view, is so much the more admissible, be- 

 cause the argonaut, by nature delicate, flexible, and submem- 

 branous, would seem to favour such a theory much more 

 readily than the nautilus. Would it then be very strange 

 that the lobes of the large arms should possess the property 

 of secreting this slender shell, and that it is but a mere mem- 

 branous pellicle in its early stage ? Do not the lobes of the 

 mantle of the Mollusca which form the cowries and the olives, 

 secrete calcareous layers, which change, in such a remarka- 

 ble manner, the original aspect of these shells, and ultimately 

 add largely to their thickness ? 



M. de Blainville, who rejects with all the weight of his 

 authority this line of argument, has, from the very first, 

 sought to re-consign the use of these membraniferous arms, 

 with which we have made him acquainted, to the wants 

 of the poulp of the argonaut, and, having so done, has pressed 

 it into the service of parasitism. Indeed this philosopher 

 points out to us, that since the poulp, as is now perfectly 



Vol. IV.— No. 37, n. s. c 



