Page:Natural History, Mollusca.djvu/238

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226
MONOMYARIA.—OSTREADÆ

among the most active members of this Class of animals; they have been called the butterflies of the shell-fishes, a comparison not less apt on account of the delicacy and beautiful colouring of the wing-like shell, than of the agile motions which they exhibit. Though inhabitants of the deep sea, these bivalves take long and rapid leaps, shooting hither and thither, and fluttering about through the water with an irregular zig-zag movement, produced by the alternate opening and shutting of the valves with great force. The motions thus performed appear to be without any determinate direction, and to depend upon the impact of the valves upon the water; but these animals (the Pectens at least) have the power of effecting a more deliberate and precise locomotion, in the performance of which the mantle is the principal agent. The following observations, which I had recently an opportunity of making upon a young specimen of the Common Scallop or Quin (P. opercularis) which I was keeping in captivity, will serve to illustrate the form and office of the foot, as well as the faculty more immediately under consideration.

My attention was attracted to the Pecten by this curious circumstance, that it was adhering by one valve (the flat one) to the side of the glass phial, at some distance from the bottom. On close examination with a lens, I discovered that it was attached by a very delicate byssus. Curious to ascertain how it contrived to mount from the bottom to this position, I touched it slightly, and caused it to loose its hold. In the course of half an hour I found that it had resumed the same position again. I again disturbed it, and began to watch its motions. It was lying with the convex