Chap, xii.] THE PEARLY NAUTILUS. 257 



it would have been if it had been obtained from a less depth, 

 the sudden change of pressure having no doubt very much 

 disarranged its economy. It, however, swam round and round 

 a shallow tub in which it was placed, moving after the manner 

 of all Cephalopods, backwards, that is with the shell foremost. 

 It floated at the surface with a small portion of the top of the 

 shell just out of the water, as observed by Rumphius. The 

 shell was maintained with its major plane in a vertical position, 

 and its mouth directed upwards. 



The floating of the shell, as described, no doubt was due to 

 some expansion of gas in the interior, occasioned by diminished 

 pressure, for the animal seemed unable to sink. It moved 

 backwards slowly by a succession of small jerks, the propelling 

 spouts from the siphon being directed somewhat downwards, 

 so that the shell was rotated a little at each stroke, upon its 

 axis, and the slightly greater area of it raised above the surface 

 of the water. 



Occasionally, when the animal was frightened or touched, it 

 made a sort of dash, by squirting out the water from its siphon 

 with more than usual violence, so as to cause a strong eddy on 

 the surface of the water. 



On either side of the base of the membranous operculum-like 

 headfold, which, when the animal is retracted, entirely closes 

 the mouth of the shell, the fold of mantle closing the gill 

 cavity was to be seen rising and falling, with a regular pulsating 

 motion, as the animal in breathing took in the water, to be 

 expelled by the siphon. 



The tentacular-like arms contrast strongly with those of 

 most other Cephalopods, because of their extreme propor- 

 tional slightness, and also their shortness, though they are not 

 shorter proportionately than those of the living Sepia. Whilst 

 swimming they are extended radially from the head, some- 

 what like the tentacles in a sea anemone ; but each pair has 

 its definite and different direction, which is constantly main- 

 tained. This direction of the many pairs of tentacles at con- 

 stant but different angles from the head, is the most striking 

 feature to be observed in the living Nautilus. 



Thus, one pair of tentacles was held pointing directly down- 

 wards. Two other pairs, situate just before and behind the 

 eyes, were held projecting obliquely outwards and forwards, and 

 backwards respectively, as if to protect the organs of sight. In 

 a somewhat corresponding manner, the tentacular arms of the 

 common cuttle-fish, whilst living, are maintained in a marked 

 and definite attitude, as may be observed in any Aquarium. 



The very great abundance of the shells of the Pearly Nautilus 

 is most strangely contrasted with the rarity of the animal 



17 



