324 MOLLUSCA.- 
The animals of the cephalopodous class, besides contain- 
ing complicated eyes, are likewise furnished withears. 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 bythe 
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- 
