CEPHALOPODA. 187 
cuttle-fishes; their superiority in number being indicative of a 
lower grade of organisation. Besides these there are four ocular 
tentacles, one behind and one in front of each eye; they seem 
to be instruments of sensation, and resemble the tentacles of 
doris 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 yalye-like fold (Fig. 51s). 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). 
Respecting 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 yery 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 hemologue of the foot of the gasteropods by Lovén, 
a conclusion with which we cannot agree. The cephalopods ought to be compared with 
the /arval gasteropods, in which 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the floating tribes in which the foot is obsolete, or serves only to secrete a nidamental 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 
ibe 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 operculigerous lobe) 
which surrounds the trochus (Fig. 114). 
