420 PHILOSOPHY OF ZOOLOGY. 



some species, it is connected with the head by an interven- 

 ing space, which may be regarded as a neck, but in others, 

 the tunic and head are continuous behind. In all, it ex- 

 hibits, after death, great changes of colour. 



On the summit of the head there is a flattened disc, in 

 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. Be- 

 yond 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 direction, and are the organs by which progressive 

 motion is performed. In the space between the head and 

 tunic in front, there is an opening or funnel with a project- 

 ing aperture. This funnel opens into the cavity of the sac, 

 and serves both to convey water to the gills, and to carry 

 off the different 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 con- 

 tains the parts which have been denominated cerebrum and 

 cerebellum, 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 pro- 

 ceed to form ganglia at the mouth, and others supply the 

 feet. The cerebellum, besides furnishing the collar which 



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