228 MONOMYARIA.—OSTREAD A. 
suspended in it, several leaps confirmed the notion 
that had suggested itself tome. The mode of pro- 
ceeding 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 mo- 
ment 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 forci- 
ble 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. 
The Oysters (Ostrea), on the other hand, are 
stationary ; never moving from the spot where the 
ege is first deposited. very 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 
