354 MANUAL OF ZOOLOGY. 



head spring a great number of muscular prehensile processes 

 or "arms," which are annulated, but are not provided with 

 cups or suckers. In the centre of the head is the mouth, sur- 

 rounded 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 calcined towards 

 their extremities, and shaped like the beak 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. 



Fig. 148. Pearly Nautilus (Nautilus pompilins). a Mantle ; b Its dorsal fold ; 

 c Hood ; o Eye ; t Tentacles ; f Funnel. 



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

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

 ratory organs are in the form of four pyramidal branchiae, 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 rudimentary 

 cranium, and which sends out processes for the attachment of 

 muscles. The organs of sense are two large eyes, attached 

 by short stalks to the sides of the head, and two hollow 



