62 M. SANDER RANG 



genera constantly possess a simple and central keel, which 

 the argonauts do not. And again, as we have long since 

 shown, the Atlanta and Carinaria are not all symmetrical in 

 form, while, on the contrary, all the argonauts are so. 



In order to prove that the argonaut is inhabited by another 

 mollusc, besides the membraniferous-armed poulp, a beauti- 

 ful specimen of this shell, in the possession of M. de Roissy 

 has been quoted, in which, by means of an accidental frac- 

 ture, a torn fragment fixed to the internal wall may distinctly 

 be perceived. We have not seen this shell, but from what 

 M. de Roissy himself has told us of it, we do not think that 

 an argument of any great weight can be drawn from this cir- 

 cumstance. Are not parasites, such as the Ascidiw, Anati- 

 Jerce, and Actinice for instance, often found (as we ourselves 

 have seen) fixed to forsaken shells ? And might they not 

 leave fragments of their base attached.? The argonaut of M. 

 de Roissy perhaps offers an example of this kind ; there is 

 nothing to prove the contrary. 



The fifth argument of M. de Blainville tends to demonstrate 

 that the form of the animal has no true correspondence with 

 that of the shell. We shall not return to this subject; for to 

 establish this correspondence is exactly what we endeavoured 

 to do towards the commencement of this memoir, and we find 

 it still greater, now that we know the use of the membranifer- 

 ous arms. 



In his ninth argument M. de Blainville expresses himself 

 thus. — "The animal may be drawn out of its shell apparently 

 without feeling any inconvenience, and without suspending 

 its movements ; as Cranch has proved positively by experi- 

 ment." Nothing is so embarrassing as. to have to refute an 

 argument, based upon what a person highly worthy of credit 

 says he has seen. We have over and over again observ^ed 

 exactly the contrary. One may combat an opinion ; but in 

 conscience one cannot tell an observer who professes to have 

 seen a thing, — "You have not seen it! \' although one may 

 feel certain that it never could have been so. We shall there- 

 fore omit the consideration of Cranch and his poulp, and 

 merely recall what we said in detailing our own observations 

 upon the one that was on the point of expiring, and which, 

 weakened, and scarcely retaining any life, had contracted its 

 membraniferous arms, and being no longer able to hold its 

 shell, was accidentally separated from it. We made the 

 same observation many years ago, upon the particular species 

 spoken of by Cranch, but with less of detail, because we did 

 not then know the use of the large arms ; and also at a later 

 period, at the Cape of Good Hope; and lastly, we have stu- 



