102 ANIMALIA MOLLUSCA. 



oesophagus ; 3, optic ganglions ; 4, lateral ganglions ; 5, ab- 

 dominal ganglion. 



Fig. B., PL 29. Anatomy of an Acephala: 1, the mouth 

 followed by the stomach and intestines ; 2, the liver ; 3, the 

 heart ; 4, the aorta ; 5, the branchiae ; 6, the muscular appa- 

 ratus ; 7, extension of the mantle in the form of a tube. 



CEPHALOPODA. 



Having the most complicated organization of all the Mol- 

 lusca; head rounded and provided with two large eyes very 

 similar to those of the vertebrated animals ; apparatus of 

 hearing situated in two little cavities, one on each side of the 

 head, without external meatus or semicircular canal, and in- 

 closing a membranous sac, in which is suspended a small 

 stone ; mouth armed with strong horny jaws, like the beak of 

 a Parrot; about its opening long fleshy arms, extremely vigo- 

 sous, capable of being flexed in every direction, and provided 

 with suckers, by means of which they attach themselves very 

 firmly to the objects which they embrace ; the rest of the 

 body inclosed in a kind of sac ; branchiae receive the venous 

 blood under the influence of the contractions of two fleshy 

 ventricles situated at the base of each ; aortic heart composed 

 of one ventricle only ; stomach extremely complicated ; a 

 peculiar gland secretes a blackish humour, which they em- 

 ploy in tinting the water of the sea for the purpose of con- 

 cealing themselves, and which is kept in a pouch diversely 

 situated according to the species. 



GENUS I. OCTOPUS, Lam. Polypus. 



Sack without the fins ; rudiments of a small dorsal, con- 

 sisting in two little grains of a horny substance, on the two 

 sides, of the thickness of the back; eight feet, nearly equal, 

 very large in proportion to the body, and united at base by a 

 membrane ; the animal uses them in crawling and seizing its 



