ILLtrSTRATED BY NAUTILUS POMPILIUS. 241 



minates in the smallest chamber at the inner extremity of the 

 "shell. I shall presently attempt to show how by means of a 

 pecuHar fluid, admitted into or abstracted from this pipe, the 

 animal has the the power to increase or diminish its specific 

 gravity, and to sink or float accordingly; as the floating 

 portion of that beautiful toy the Water balloon is made to 

 descend or ascend by means of water forced into, or ab- 

 stracted from its interior. (See P. 248.) 



The motion of the Nautilus, when swimming, with its arms 

 expanded, is retrograde, like that of the naked Cuttle Fish, 

 being produced by the reaction of water, violently ejected 

 from the funnel (k.) 



The position assumed during this operation is that which 

 is best adapted to facilitate its passage through the water, 

 as it places foremost that portion of the shell, which ap- 

 proaches most nearly in form to the prow of a boat. The 

 fingers and tentacula (p, p,) are here represented as closed 

 around the beak, which is consequently invisible; when the 

 animal is in action, they are probably spread forth like the 

 expanded rays of the sea Anemone. 



The horny beak of this recent Nautilus (See PI. 31, Fig. 

 2, 3) resembles the bill of a Parrot. Each mandible is 

 armed in front, with a hard and indented calcareous point, 

 adapted to the office of crushing shells and crustaceous ani- 

 mals, of which latter, many fragments were found in the 

 stomach of the individual here represented. As these be- 

 longed to species of hairy brachyurous Crustacea, that live 

 exclusively at the bottom of the sea, they show that this 

 Nautilus, though occasionally foraging at the surface, ob- 

 tains part of its food from the bottom. As it also had a giz- 

 zard, much resembling that of a fowl, we see in this organ, 

 farther evidence that the existing Nautilus has the power of 

 digesting hard shells.* 



• In Pl. 31, Fig. 3 represents the lower mandible, armed in front like 

 Fig. 2. with a hard and calcareous margin; and Fig. 4 represents the anterior 

 calcareous part of the palate of the «pper mandible Fig. 2. formed of the 



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