Page:Natural History, Mollusca.djvu/240
The Oysters (Ostrea), on the other hand, are stationary; never moving from the spot where the egg is first deposited. Every one is aware that the shells are frequently found adhering in the firmest manner to rocks or stones, or to each other; the substance of the shell having been deposited upon the foreign body, so as to conform perfectly
suspended in it, several leaps confirmed the notion that had suggested itself to me. The mode of proceeding is as follows: when the Pecten is about to leap, it draws in as much water as it can contain within the mantle, while the lips are held firmly in contact. At this instant the united edges of the lips are slightly drawn inward, and this action gives sure warning of the coming leap. The moment after this is observed, the animal, doubtless by muscular contraction, exerts a strong force upon the contained water, while it relaxes the forced contact of the lips at any point of the circumference, according to its pleasure. The result is, the forcible ejection of a jet of water from that point; which, by the resilience of its impact upon the surrounding fluid, throws the animal in the opposite direction, with a force proportioned to that of the jet d'eau. The action may be well imitated by the human mouth blowing a stream of air from any determined point, while the lips are held firmly together at all other points. The resemblance, indeed, of the mantle to the human lips performing such an action, (a resemblance perhaps more close than flattering,) struck me as ludicrously faithful. Nor was the appearance less suggestive of a pair of bellows without a nose, of which the valves were the covers, and the mantle the leathers, discharging their contents from any part of their sides.