OCYTHOID2E. 
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 Lamch. Phil. Zool. i. 322. 1809. 
Ceph. Argon autidae Cantraine , Mall. Medit. 13. 1841. 
Ceph. Argonautica Gravenhorst, Thier. 1845. 
Philonexidae (pars) D' Orb. 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. 
