CEPHALOPODA. 187 



CTittle-fisLes ; their superiority in number being indicative of a 

 lower grade of organisation. Besides these there are four ocular 

 tentadeSy one behind and one in front of each eye ; they seem 

 to be instruments of sensation, and resemble the tentacles of 

 dor is and aplysia. (Owen.) On the side of each eye is a hollow 

 plicated process, which is not tentaculiferous. This process 

 bears the external ears. The cavity leads to the auditory cap- 

 sule, along a passage lined with a glandular membrane. The 

 respiratory funnel is formed by the folding of a very thick 

 muscular lobe, which is prolonged laterally on each side of the 

 head, with its free edge directed backwards into the branchial 

 cavity ; behind the hood it is directed forwards, forming a lobe 

 which lies against the black-stained spire of the shell (Fig. 50 s).* 

 Inside the funnel is a valve-like fold (Fig. 51 s). The margin 

 of the mantle is entire, and extends as far as the edge of the 

 shell : 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 narrow 

 tract across the hollow occupied by the involute spire of the 

 shell : and are thus rendered horse- shoe shaped. The siphuncle 

 is vascular ; it opens into the cavity containing the heart {peri- 

 cardium), and is most probably filled with fluid from that 

 cavity (Owen). 



Eespecting the habits of the nautilus very little is known : 

 the specimen dissected by Professor Owen had its crop filled 

 with fragments of a small crab, and its mandibles seem well 

 adapted for breaking shells. The statement that it visits 

 the surface of the sea of its own accord is, at present, uncon- 

 firmed on observation, although the air-cells would doubtless 

 enable the animal to rise by a very small amount of muscular 

 exertion. 



Professor Owen gives the following passage, from the old 

 Dutch naturalist, Rumphius, who wrote, in 1705, an account of 

 the rarities of Amboyna. " When the nautilus floats on the 

 water, he puts out his head and all his tentacles, and spreads 

 them upon the water, with the poop of the shell above, water ; 



* The funnel is considered to be the homolop^ue of the foot of the gasteropods by Loven, 

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

 the larval gasteropods, in which the foot only serves to support an operculum; or with 

 tlie floating tribes in which the foot is obsolete, or serves only to secrete a nidamental 

 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 extends all round 

 the neck of the animal, we could not avoid noticing its resemblance to the siphonal 

 lappets of paludina, and to that series of lappets (including the opercidigerous lobe) 

 wtiich surrounds the trochus (Fig. 114). 



