546 



CEPHALOPODA. 



According lo Aristotle the hard dorsal body 

 of the Cuttle-fish was called by the Greeks 

 1 sepion,' that of the Calamaries * xiphos.'* 

 In Sepiola and Rossia the gladius does not 

 reach half-way down the back, beginning at 

 the anterior margin of the mantle, which in 

 the latter genus is free. In Loligopsis, Cran- 

 chia, Onycoteut/iis, and Loligo, it extends 

 the whole length of the posterior part of the 

 mantle. In Sepioteuthis it rivals in breadth 

 the Sepium or Cuttle-bone, but is horny and 

 elastic, as in the Calamary. In the latter the 

 gladius is multiplied by age, and several are 

 found packed closely one behind another in 

 old specimens. 



Fig. 229. 



Gladius of the 

 Calamary. 



Rudimental Shell of the 

 Cuttle-fish. 



The Sepium or Cuttle-bone (fig. 229) is a 

 well-known substance, and formerly figured in 

 the Materia Medica as an antacid. It is a 

 light cellular calcareous body, of a peculiar 

 form and structure ; and, as it is confined ex- 

 clusively to the genus Sepia, its presence alone 

 serves to characterise that section of Cepha- 

 lopods. Its form is an elongated oval, de- 

 pressed, convex on the dorsal surface, partly 

 convex and partly concave on the opposite 

 side: it terminates posteriorly in a very thin, 



* " TB /uv ovV o-r,in'itt, x.al -rn ttvi xa tm rt 



IvW? fl Ttt <TTEp EV Tfl5 TTpetVei TOV r&flCtTQG, 3. Xtt- 



Xotlm TO /U.EV sri-Triov, T Si /<f>o$. Sub dorso firma 



Ears Sepiae Loligini ac Lolio continetur ; i\\ius sepium, 

 orum gladuim vocant- Hist. Animal., lib. iv., c. 1. 

 12mo. Ed. Schneider. 



dilated, aliform margin (a, a), partly calca- 

 reous and partly horny, which becomes nar- 

 rower as it advances forwards, and is gradually 

 lost in the sides of the shell. As this margin 

 is inclined towards the ventral aspect, it pro- 

 duces at the posterior and ventral side of the 

 shell a wide and shallow concavity, comparable 

 to the chamber of the Nautilus shell which 

 protects the body of that species : if the free 

 margin of the sepium were in like manner 

 produced beyond the previously deposited 

 layers, it would advance from the posterior and 

 lateral aspects of the animal, and cover the 

 ventral surface, as in the Nautilus, leaving the 

 convexity produced by the chambered portion 

 projecting into the back. The thickened part 

 of the sepium (6) which retains that situation, 

 is in fact composed of a series of thin parallel 

 calcareous plates, successively deposited and 

 extending obliquely forwards from the ventral 

 to the dorsal surface : the last formed plate is 

 the most internal and the broadest, but not the 

 longest also, as in the Nautilus ; its develop- 

 ment being limited to the anterior part of the 

 shell, so that the previously deposited layers 

 appear successively behind it forming irregular 

 sinuous transverse striae (c). The intervals of 

 the plates are occupied by crystalline fibres, 

 passing perpendicularly from one layer to the 

 other : A is a magnified view of this structure. 

 At the posterior part of the sepium, a little 

 anterior to the thin margin, a pointed hooked 

 process projects backwards : this differs m size 

 and shape in different species of Sepia; but it is 

 always characteristic of the peculiar production 

 which has been described, and has served to 

 identify some doubtful fossils. 



As our present observations are limited to 

 the recent species of Cephalopoda, we pass 

 over the Belemnites, which are fossil internal 

 shells of extinct animals of this order, to speak 

 of that of the Spirula. This is a small recent 

 Cephalopod, respecting the precise form and 

 organization of which nothing is yet satis- 

 factorily known. The only entire specimen 

 which has been brought to Europe was taken 

 by Peron, a French Naturalist, as it floated 

 dead in the Tropical Ocean, between the Mol- 

 luccas and the Isle of France ; it has been de- 

 scribed and figured by Roissy, Peron, and 

 Lamarck ; but both the figures and descrip- 

 tions of these authors differ, and the specimen 

 now no longer exists to determine the accuracy 

 of either of the accounts. All agree, how- 

 ever, in stating that part of the shell was 

 concealed within the body of the animal ; and 

 this fact is confirmed by a mutilated specimen 

 in our own possession, and by one in a similar 

 condition in the British Museum. 



The shell of the Spirula (jig. 230) is about 

 an inch in diameter, 



symmetrical, con- 

 voluted on one 

 plane, with the 

 whorls disjoined : 

 it is composed of a 

 succession of small 

 regularly formed 



Fig. 230. 



Shell of the Spirula. 



chambers, separated by partitions (, ), which 



