ocYTHonxa:. 29 



position on the body. Unlike all other Mollusca, which form 

 the shell they inhabit : First, the Ocythoe is not attached to the shell 

 by any muscle, nor has it any muscle, like the bone-bearing cuttle- 

 fish, formed for the purpose of attaching the body to an internal 

 shell. Secondly, the animal, when alive, does not fit the shell ; so 

 that the shell cannot have been moulded on its body, as in other 

 Mollusca. Thirdly, the skin of the Ocythoe is of the same texture 

 and appearance as in the other naked Cephalopoda ; and the presence 

 of sand between the shell and the body appears to cause no un- 

 easiness to the animal, as it does in all other shell-bearing Mol- 

 lusca, where the animal immediately rids itself of the irritation 

 so caused by covering the sand, &c, with a calcareous coat. 

 The animals found in these shells are always female, and the 

 apex of the shell is filled with very small eggs ; while from the 

 large size of the young shell, which is seen on the apex of the true 

 Argonaut, we should expect the animal which formed that shell 

 to have a large egg : for, though the eggs of Mollusca are enlarged 

 during the hatching, they are not, in any case I have observed, so 

 much enlarged as to have such a shell. 



It is supposed by those who believe that the shell belongs to 

 the Ocythoe, that it is formed and mended when broken by 

 the expanded ends of the upper arms, which embrace the outer 

 surface of the shell, and keep it on the body of the animal. 



Cranch and Adams, who have seen these animals alive, state 

 that they leave the shell when they are frightened, and they cannot 

 recover their position in the shell after they have thus left it. 



Mr. Adams regards the Argonaut shell as a nest formed by 

 the female to contain her eggs ; if this is correct, it can scarcely be 

 compared to other shells. He regards them as similar to the carti- 

 laginous cases which Murices and other zoophagous Mollusca form 

 to contain their eggs ! ; but they have no apparent analogy to those 

 bodies, which are secreted by the oviduct as the eggs are deposited. 



These various views show that the origin of the shell is not yet 

 distinctly settled. 



Living on the high seas, floating, and feeding on floating Mol- 

 lusca. 



Cephalopoda testacea (pars) Cuvier, Anat. Comp. 1800. 

 Cephalopoda testa unilocularia Launch. Phil. Zool. i. 322. 1809. 

 Ceph. Argonautidas Cantraine, Mall. Medit 13. 1841. 

 Ceph. Argonautica Gravejihorst, Thier. 1845. 

 Philonexidae (pars) UOrb. Moll. Viv. et Fos. i. 199. 1845. 

 C. cymbicochlides (pars) Latr. Fam. Nat. 168. 1828. 

 C. octopia and C. argonautea Rafin. Anal. Nat. 1815. 

 Cephalopodes monothalmes Lamch. Hist. ed. 2. 171. 343. 

 Ocythoina Gray, Proc. Zool. Soc. 1847. 204. 



c 3 



