capsule of the laminated calcareous plate. In Nautilus they attain their highest 

 degree of development, and correspond in bulk and strength to the capacity and 

 weight of the testaceous covering. 



In this way a clue is obtained to the true nature of the several incysted sub- 

 stances above mentioned, which, from being buried in the mantle, have fre- 

 quently been considered the analogues of the internal skeletons of the Vertehrata. 

 But the true skeleton of the Cephalopoda is the internal cartilaginous part which 

 gives origin to the muscular, and protection to the nervous system, and accord- 

 ingly we find that this part, like the skeleton of the Vertehrata, maintains, both 

 with respect to its composition and situation, a characteristic constancy through- 

 out the whole class. Whilst, on the other hand, the friable styles, the horny and 

 calcareous plates, manifest, in this verj^ diversity of character, their relation to the 

 dennal system, which in every class of animals is the cliief seat of varieties. 



Ha^ing found in the genera above described so close a correspondence in 

 the mode of attachment of the shell to the body, in whatever degree of de- 

 velopment it existed, it became extremely desirable to examine the other genus 

 of Cephalopoda, which, hke Nautilus Pompilius, has an external shell, viz. the 

 Paper Nautilus, or Nautilus primus of the ancients, the Argonauta and Ocythoe 

 of the moderns ; an animal concerning which a difference of opinion has long 

 subsisted among naturalists, as to whether the shell it inhabits be or be not se- 

 creted by it. For the means of examining this species I am indebted to W. J. 

 Broderip, Esq. and Captain P. P. King, R.N. ; the former gentleman having, 

 with his usual zeal for science, pennitted me to dissect the beautiful and well- 

 preserA-ed specimen described by him, and figured in the first volimie of the 

 Zoological Journal ; and the latter gentleman having placed at my disposal 

 several small, but equally perfect specimens, which, together with the shells in 

 question, were taken by him out of the stomach of a dolphin. 



In these specimens I found that every trace of internal shell had disappeared. 

 Of the muscles that are attached to the capsules of the friable styles of Octopus, 

 those which Cuvier has termed, in the Memoir above quoted, " les gros piliers 

 laterals de I'entonnoir", were smaller than in Octopus, were round and slender, 

 and terminated posteriorly by blending with the inner fibres of the mantle. The 

 muscles really analogous to the shell-muscles of Nautilus were reduced to a few 

 fibres, accompanying and still manifesting a relation to the ganglion stellatum, 



