Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/245

 Rh in the smallest chamber at the inner extremity of the shell. By means of this pipe, the animal has power to increase or diminish its specific gravity, as Fishes do, by distending their membranous air bladder with air, or by causing it to collapse. When the pipe of the Nautilus is filled with any fluid, the weight of that fluid, being added to the body and shell, renders the mass specifically heavier than water, and the animal sinks. When it is inclined to rise, it withdraws the fluid from the pipe, and thus again, becoming specifically lighter, rises upwards to the surface.

The motion of the Nautilus, when floating, 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 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 Pl. 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 animals, of which latter, many fragments were found in the stomach of the individual here represented. As these belonged to species of hairy brachyurus crustacea, that live exclusively at the bottom of the sea, they show that this Nautilus, though occasionally foraging at the surface, obtains part of its food from the bottom. As it also had a gizzard, much resembling that of a fowl, we see in this organ, further evidence that the existing Nautilus has the power of digesting hard shells.

A similar apparatus is shown to have existed in the beaks