CEPHALOPODA. 85 



on their inner surface, and are retractile within sheaths, or " digitations," 

 which correspond to the eight ordinary arms of the cuttle-fishes ; their supe- 

 riority in number being indicative of a lower grade of organization. Besides 

 these there ai'e four ocular tentacles, one behind and one in front of each eye ; 

 they seem to be instrimients of sensation, and resemble the tentacles of doru 

 and aphjsia {Owen). On the side of each eye is a hoUow plicated process, 

 which is not tentaculiferous. The respiratory funnel is formed by the folding 

 of a very thick muscidar lobe, which is prolonged laterally on each side of the 

 head, with its free edge directed backwards, into the branchial ca\dty ; behind 

 the hood it is directed foi-wards, forming a lobe which lies against the black- 

 stained spire of the shell (fig. 43 J.)* Inside the funnel is a valve-like fold 

 (fig. 44 s). The margin of the mantle is entire, and extends as far as the 

 edge of the sheU ; its- substance is firm and muscular, as far back as the line 

 of the shell-muscles and horny girdle, beyond which it is thin and transparent. 

 The shell-muscles are united by a naiTow tract, across the hollow occupied by 

 the involute spire of the shell ; and are thus rendered horse-shoe shaped. 

 The siphuncle is vasculai" ; it opens into the cavity containing the heart ( pe- 

 ricardium), and is most probably filled with fluid from that cavity. {Owen.) 



Respecting the habits of the nautilus, very little is known, the specimen 

 dissected by Professor Owen had it crop filled mth fragments of a small crab, 

 and its mandibles seem well adapted for breaking shells. The statement that 

 it visits the sm^ace of the sea of its own accord, is at present unconfirmed 

 by observation, although the air cells would doubtless enable the animal to 

 rise by a veiy small amount of muscular exertion. 



Professor Owen gives the following passage, from the old Dutch natm-alist, 

 Rmnphius, who wrote in 1705, an accomit of the rai-ities of Amboina. 

 " When the nautilus floats on the water, he puts out his head and all his tenta- 

 des, and spreads them upon the water, with the poop of the shell above water ; 

 but at the bottom he creeps in the reverse position, with his boat above him, 

 and with his head and tentacles upon the ground, making a tolerably quick 

 progress. He keeps himself chiefly upon the ground, creeping also sometimes 

 into the nets of the fishennen ; but after a stonii, as the weather becomes 

 calm, they are seen in troops, floating on the water, being driven up hy the 

 agitation of the ivaves. This sailing, however, is not of long continuance ; 



* The fim}iel is considered the homolo!?ue of the foot of the gasteropods, by Loven, 

 a conclusion to which we cannot agree. The cephalopods ought to be compared with 

 the larval gasteropods, in whicli the foot only serves to support an operculum; — or 

 with the floating tribes in which the foot is obsolete, or serves only to secrete a nida- 

 niental raft {ianthina). However, on examining the nautilus preserved in the British 

 Museum, and finding that the funnel was only part of a muscular collar, which ex- 

 tends all round the neck of the animal, we could not avoid noticing its resemblance 

 to the siphonal lappets oi paludina, and to that series of lappets (including the oper- 

 culigerous lobe) which surrounds the trochus (fig. 87). 



