124 MOLLUSC A. 



The animals of the cephalopodous class, besides contain- 

 ing complicated eyes, are likewise furnished with ears. These 

 are situate in the annular cartilage which supports the arms. 

 In this cartilage, there are two cavities, in each of which 

 there is a bag filled with a gelatinous, transparent fluid, and 

 containing a calcareous substance, differing in its consis- 

 tence according to the species, from the brittleness of starch 

 to the hardness of bone. The auditory nerve penetrates 

 the walls of this labyrinth, and ramifies on the membran- 

 ous bag which it contains. There is no external opening, 

 nor any apparent alteration in the thickness of the invest- 

 ing integuments. 



The digestive system of the Cephalopoda exhibits seve- 

 ral appearances by which it may be distinguished. The 

 arms which surround the mouth, seize the animals which 

 are to serve as food, and bring them to the mouth. The 

 mouth is situated in the centre of the disc, round which the 

 tentacula are arranged. It is surrounded with a slight fold 

 of the skin, which may be compared to lips, and which is 

 rough on the central aspect. Within the lips are the two 

 mandibles, of a deep brown colour, hard, horny consistence, 

 and in form resembling the beak of a parrot. Where free, 

 they are conico-tubular, but where covered, they are open 

 at the central side. The under beak, unlike the same 

 organ in birds, is the largest, the most crooked, and em- 

 braces the upper, or the one on the dorsal margin of the 

 mouth. These jaws are merely able to open and shut, as 

 they possess no lateral motion. They are supported by the 

 muscular bed of the mouth, which serves as a mould to fill 

 the cavity towards the point. The tongue is situate be- 

 tween the beaks, and is armed with reflected teeth. These 

 teeth, in consequence of the undulatory motion of the sub- 



