MOLLUSCA. 121 



the centre of which is seated the mouth. Round the mar- 

 gin of this oral disc, which is strengthened by a band of 

 muscular fibres, are placed the arms or tentacula. Beyond 

 this circle of arms, in some species, there are situated two 

 organs, larger in their dimensions than the arms, which may 

 be denominated feet. Both the arms and feet are covered 

 on their central aspect with numerous suckers, by which 

 they are enabled to attach themselves to different bodies, 

 and to seize their prey ; and in their axis, both a nerve and 

 artery may be observed. These arms and feet are capable 

 of being moved, at the will of the animal, in every direc- 

 tion, and are the organs by which progressive motion is per- 

 formed. In the space between the head and tunic in front, 

 there is an opening or funnel with a projecting aperture. 

 This funnel opens into the cavity of the sac, and serves 

 both to convey water to the gills, and to carry off the differ- 

 ent excreted matters. 



The brain in the Cephalopoda is contained in an irregu- 

 lar hollow ring, in the cartilaginous border of the oral disk. 

 This cartilage is thickest on the dorsal aspect, and contains 

 the parts which have been denominated cerebrum and cere- 

 bellum, the remaining part of the canal being occupied with 

 the collar, which surrounds the esophagus. The nerves, 

 which proceed directly from the brain to the parts which 

 they are destined to influence, are few in number. From 

 the cerebrum a few small nerves issue, which go to the 

 mouth, and the base of the feet, while some proceed U, 

 form ganglia at the mouth, and others supply the feet. The 

 cerebellum, besides furnishing the collar which encircles 

 the gullet, contributes to the formation of the large ganglia 

 which supply the arms, the optic and auditory nerves, 

 those for the funnel, the tunic, and the viscera. From the 



