MOLLUSCA CEPHALOPODA. 235 



part of tlie animal which has produced it ; but is 

 enclosed in a capsule, and appears like a foreign 

 body, impacted in the midst of organs, with which 

 at first sight, it would appear to have no relation. 

 It, no doubt, is of use in giving mechanical support 

 to the soft substance of the body, and especially to 

 the surrounding muscular flesh ; and thus probably 

 contributes to the high energy which the animal 

 displays in all its movements. It has been re- 

 garded as an internal skeleton ; but it certainly has 

 no pretensions to such a designation ; for, although 

 enveloped by the mantle, it is still formed by that 

 organ, and the material of which it is composed is 

 still carbonate of lime. On both these accounts it 

 must be considered as a true shell, and classed 

 among the productions of the integuments. It 

 differs, indeed, altogether from bony structures, 

 which are composed of a difterent kind of material, 

 and formed on principles of growth totally dis- 

 similar.* 



Besides tentacula, the Sepia is also furnished 

 with a pair of fleshy fins, extending along the two 

 sides of the body. The Loligo has similar organs 

 of a smaller size, and situated only at the ex- 

 tremity of the body which is opposite to the head. 

 They have been regarded as the rudiments of true 

 Jins, which are organs developed in fishes, and 



* Some analogies have, indeed, been attempted to be traced 

 between the cartilaginous lamina of the Loligo, and the spinal 

 column of the lowest order of cartilaginous fishes : these I shall 

 have occasion to point out in the sequel. Several cartilaginous 

 structures also exist in the interior of the body of the cephalopoda, 

 which are considered by Meckel and Carus as indicating an approach 

 to the formation of an internal skeleton, analogous to that of verte- 

 brated animals. 



