442 



CEPHALOPODA. 



Fig. 206. 



shells, by the continued addition of calcareous laminae secreted by 

 that side of the containing capsule which is interposed between the 

 shell and the abdominal viscera ; and these layers, being successively 

 added to the ventral surface of the shell, thus gradually increase its 

 bulk as the Cuttle-fish advances to maturity. Neither in the mode 

 of its growth nor in its texture, therefore, does the os Sepice resem- 

 ble bone, properly so called ; it receives neither vessels nor nerves, 

 but is in all respects a dermal secretion, imbedded in the mantle, 

 and formed in the same manner as the dorsal plate of the Slug. 



(485.) We 

 now come to 

 consider the 

 long disput- 

 ed question 

 relative to the 

 nature of the 

 shell of the 

 Argonaut. 

 The Poulpe 

 that inhabits 

 the elegant 

 abode repre- 

 sented in a 

 preceding fi- 

 gure ( Jig. 

 204), when 

 removed from 

 its testaceous 

 covering, has 

 the general 

 form of an 

 Octopus. Its 

 body (Jig. 

 206) is en- 

 closed in an 

 ovoid mus- 

 cular sac (d), 

 and the head 



is surmounted by eight long sucker-bearing arms, of which six 

 (e,/)taper gradually from their origins to their extremities, while 

 the other two, formerly regarded as sails, and which we shall con- 



d 



