104 OBSERVATIONS ON THE ARGONAUT. 



removes tliem, and spreading, raises them in the office of sails. 

 In fact, the series of suckers of the sail-arms, when the mem- 

 brane of the sails is wrapped about the shell, are placed ex- 

 actly over the keel of it, in such a manner that each sucker 

 corresponds to each point in which the ribs of the argonaut 

 terminate until they reach the two margins of the spiral. 



Observation leads me to compare the sails of the argonaut 

 with the two wings of the mantle of the Cyprcea, not only 

 from the manner in which they cover the shell, but because I 

 have reason to believe that the formation itself of the shell 

 results from a transudation by the membrane of the sails, 

 the corrugations of which, in secreting the calcareous matter, 

 may be the cause of the ribbed form of the shell. These may 

 also serve as a means of retention of the animal in its shell 

 during the movements of the mollusc, which, without all these 

 furrows, might easily slip about from one side to the other. 



This consideration may weigh in obviating the difficulties 

 of those who cannot imagine how a shell containing a cepha- 

 lopod should present no resemblance with the folds of the 

 animal compressed within it. For if they would consider it 

 the result of a calcareous deposition of the membrane of the 

 sails, they would find not only the series of little points cor- 

 responding to the suckers, which adapt themselves to the keel 

 of the spiral, but an explanation of the disposition of the ribs, 

 and of the smooth and paper-like condition of all the shell. 

 They have not all seen, I can frankly assert, how the argonaut 

 appears when it has placed its sails over the shell ; drawing 

 alone can shew it, and I have here annexed a figure which is 

 a very good resemblance. 



The sail when spread out presents a silvery surface, speck- 

 led with concentric circles of spots with a black spot in the 

 middle, and surrounded with a beautiful gold colour; and 

 this and the vicinity of the suckers along the keel and the 

 spiral assume so vivid a purple colour that it approaches that 

 of the Ianthina. 



The mouth, the head, the bag, and the branchia, have not 

 presented me with any particularity but what has been alrea- 

 dy well described by naturalists, and which is common to the 

 Sepia and Calamaries, in these parts little differing from my 

 argonaut. However, as regards the funnel with which these 

 cephalopods are furnished, I believe I have two new obser- 

 vations to offer. One is, that it holds the office of a pump or 

 proboscis, rather than that of a funnel ; and that the animal 

 employs it, when swimming with its arms on the surface of the 

 water, as a helm, elongating it in front of the widest part of 

 the shell, at the same time that the spiral serves as a prow. 



