MOLLUSGA. 12] 
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 to 
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 
G 
