Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/253

 Rh floating at the surface, with the upper portion of the shell raised above the water, and kept in a vertical position by means of the included air (see Pl. 31. Fig. 1.); this position is best adapted to the retrograde motion, which a Sepia derives from the violent ejection of water through its funnel (k); thus far, the air-chambers, serve to maintain both the shell and body of the animal in a state of equilibrium at the surface.

Secondly, The next point to be considered is the mode of operation of the siphuncle and air-chambers, in the act of sinking suddenly from the surface to the bottom. These are explained in the note subjoined.