TETRABRANCHIATE CEPHALOPODS. 



61 



mouth, surrouuded by a circular fleshy lip, external to which 

 is a series of labial processes. The mouth opens into a 

 buccal cavity, armed with two horny mandibles, partially 

 calcified towards their extremities, and shaped like the beak 



-Pearly Nautilus (Naiitihis pompilnis). a, Mantte ; 6, Its dorsal fold ; 

 c, Hood ; 0, Eye; t, Tentacles ; /, Funnel. 



of a parrot, except that the under mandible is the longest. 

 There is also a " tongue," which is fleshy and sentient in 

 front, but is armed with recurved teeth behind. The gullet 

 opens into a large crop, which in turn conducts to a gizzard, 

 and the intestine terminates at the base of the funnel. On 

 each side of the crop is a well-developed liver. 



The heart is contained in a large cavity, divided into several 

 chambers, and termed the "pericardium " (Owen). The res- 

 piratory organs are in the form of four pyramidal branchia?, 

 two on each side. 



The chief masses of the nervous system are the cerebral 

 and infra-cesophageal ganglia, which are partially protected 

 by a cartilaginous plate, which is to be regarded as a rudi- 

 mentary cranium, and which sends out processes for the 

 attachment of muscles. The organs of sense are two large 

 eyes, attached bv short stalks to the sides of the head, and 



