Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/244

 240 the economy of millions of creatures long since swept from the face of the living world. From the similarity of these mechanisms to those still employed in animals of the existing creation, we see that all such contrivances and adaptations, however remotely separated by time or space, indicate a common origin in the will and design of one and the same Intelligence.

We enter then upon our examination of the structure and uses of fossil Chambered shells, with a preliminary knowledge of the facts, that the recent shells, both of N. Pompilius and Spirula, are formed by existing Cephalopods; and we hope, through them, to be enabled to illustrate the history of the countless myriads of similarly constructed fossil shells whose use and office has never yet been satisfactorily explained.

We may divide these fossils into two distinct classes; the one comprising external shells, whose inhabitants resided like the inhabitant of the N. Pompilius, in the capacious cavity of their first or external chamber (Pl. 31, Fig. 1;) the other, comprising shells, that were wholly or partially included within the body of a Cephalopod, like the recent Spirula, (Pl. 44, Figs. 1, 2.) In both these classes, the chambers of the shell appear. to have performed the office of air vessels, or floats, by means of which the animal was enabled either to raise itself and Boat near the surface of the sea, or sink to the bottom.

It will be seen by reference to Pl. 31, Fig. 1, that in the recent Nautilus Pompilius, the only organ connecting the air chambers, with the body of the animal, is a pipe, or siphuncle, which descends through an aperture and short projecting tube (y) in each successive transverse plate, till, it terminates