INTERPRETATION OF THE SHELL IN RECENT CEPHALOPODS. 291 



r. 



-r. 



The lamellae are connected by numerous delicate calcareous trabeculae, so 

 that the spaces between them are not empty, as one might expect if they 

 represented chambers. But this can hardly be reckoned as an argument 

 against the above interpretation of the Sepia shell, as such a modification of 

 the shell iu adaptation to new functions (as a float) is quite explicable. 



The development of the different parts of the Sepia shell has been investi- 

 gated in detail by APPELOFF, but has, so far as we know, been described only 

 in a short Swedish treatise (No. 2) from which it is impossible to judge 

 whether factors of import- 

 ance for the morphological v 

 interpretation of the shell cA) 

 have been discovered. 



Finally, it appears neces- 

 sary to point out that this 

 whole comparison is still 

 far from being well founded, 

 although it may be con- 

 sidered as extremely 

 plausible. 



Other recent Cephalo- 

 pods, especially thosewhich 

 are universally regarded 

 as more primitive than 

 Si'/>ia, have a shell of very 

 simple structure, carrying 

 at its end at the most a 

 hollow cone (Ommastrephes, 

 Fig. 140). If this structure 

 is compared with the phrag- 

 mocone, the rest of the 

 shell would have to be 

 regarded as the proostra- 

 cum, and this suggests the 

 idea that, in Sepia also, 

 the fork which bifurcates 

 anteriorly and the con- 

 tained cavity may be 

 regarded as such a much- 

 reduced phragmocone. The 

 whole of the part lying 

 anteriorly to it (the prominence) would then have to be considered as the 

 proostracum, which has perhaps attained such a large size in adaptation 

 to its present function, the diminution of the specific gravity of the body. 

 The lamellate structure of the prominence would then be traceable to a 

 secondary modification causing the secretion of the shell in layers, to form 

 the air-cavities of the float ; under these circumstances the higher morpholo- 

 gical significance could not be ascribed to it. Further light upon the subject 

 of the significance of the shell of Sepia and its relation to the shells of the 



,T 



FIG. 138. A, Diagrammatic longitudinal section of 

 the shell of Sepia; B, shell of Belosepia Blain- 

 mllei, seen from the side ; C, posterior part of the 

 same, seen from the ventral side (B and C after 

 ZITTEL). d, spine ; ph, phragmocoue ; r, rostrum ; 

 5, siphon ; w, prominence. 



