ON, THE ARGONAUT. 59 



they are in the water ; it is there only that they enjoy the fa- 

 culties for action which have been given them ; and in the 

 water we affirm that they never crawl or progress in the man- 

 ner above described, any more than that they swim in turning 

 upon themselves, as has been advanced. 



We do not however altogether disallow the force of the ar- 

 gument advanced by M. de Blainville, and this is the way in 

 which we understand it. If we suppose that a poulp, from 

 the nature of its exigences, saad' from its peculiarly pelagian 

 destiny,- is compelled to have recourse to a shell in which to 

 lodge itself, and pass the whole or a part of its life, we must 

 certainly admit, in some of its organs, a particular pre-arrange- 

 ment or modification. It would, for example, be necessary 

 that nature should have provided it with organs specially des- 

 tined to maintain its position within this foreign covering ; — 

 and such organs we find in the membraniferous arms of the 

 poulp we are now considering. Thus, when we meet with 

 an animal surrounded by these peculiarities,- — a mollusc in 

 this anomalous state, — we may be justified in considering it 

 to be a parasite, but can we affirm with certainty that it is so? 

 It is after all but a pjesumption ; and to consider the para- 

 sitism demonstrated, would perhaps be hardly compatible 

 with sound logic. 



We cannot conclude this portion of our memoir without 

 remarking that Ferussac, a short time before his death, as we 

 have just learned, entertained the idea that the membranifer- 

 ous arms of the poulp of the argonaut were disposed by the 

 poulp upon the lateral faces of the shell ; this, at least, is 

 what we found expressed in a letter, written by him to M. 

 Pretre, requesting from him a new plate for his great work on 

 the cryptodibranchiate cephalopods, and which letter that 

 skilful artist very willingly communicated to us. The pas- 

 sage is as follows. — "In the second phial is a specimen in its 

 shell (of which also a view must be taken), and having the 

 large membrane very much spread out with great care over 

 the shell, in the same position as its arm." Unfortunately,, 

 neither the animals nor the beautiful drawing made by M. 

 Pretre are to be found; and the sentence we have just quoted 

 is all that we possess by Ferussac relating to a subject which 

 it would have been very interesting to see treated of by him. 



Locomotive Faculty of the Argonaut in deep water. — When 

 in deep water the poulp of the argonaut swims in the same 

 manner as other cryptodibranchial cephalopods, — by the re- 

 jection of the water introduced into the sac by means of a 

 tube situated opposite to the anus. Such is the third obser- 



