Page:Popular Science Monthly Volume 20.djvu/472

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body; and their form has given to this class the scientific name Lamellibranchiata—plate-gills. The water bathing the gills is constantly renewed by means of cilia. "Wonderful, indeed, is the elaborate mechanism employed to effect the double purpose of renewing the respired

PSM V20 D472 Lamellibranch showing two siphons.jpg
Fig. 11.—Lamellibranch, showing two Siphons. (After Horse.)

fluid and feeding the helpless inhabitants of these shells. Every filament of the gill-fringe, examined under a powerful microscope, is found to be covered with countless cilia, in constant vibration, causing, by their united efforts, powerful and rapid currents. ... So energetic,

PSM V20 D472 Tracheal system of a water bug and of the larva of an aeschna.jpg
Fig. 12.—Tracheal System indicated within the Outline a of a Water-Bug, b of the Larva of an Æschna. The tracheæ are shaded.

indeed, is this ciliary movement over the entire extent of the branchial organs that, if any portion of the gills be cut off with a pair of scissors, it immediately swims away, and continues to row itself in