Oysters and Scallops 79 



its succeeding growth will in all probability greatly 

 modify this form. At an early stage of existence 

 the left valve becomes cemented to a stone, an older 

 shell, or to some other object on the bottom, and 

 thenceforward remains a fixture. It has, therefore, 

 no need of a foot either for locomotion or for spinning 

 a byssus, and the foot is absent. The mantle has a 

 double margin with a fine fringe ; the lips are large 

 and nearly triangular. In the adjoining figure it 

 will be seen that the solitary muscle for closing the 

 valves is placed nearly in the centre of the shell. In 

 the species considered in the previous chapter there 

 were two such muscles, one at each end of the shell 

 but away from the beaks. In Finna, though these 

 muscles appear to have changed their positions, it is 

 really the beaks that have moved to the extreme 

 front of the shell. In Ostrea, one muscle has entirely 

 gone, but the remaining one is much enlarged. There 

 is a thick, strong, curved pad of cartilage between the 

 beaks to keep the valves open, and a short ligament 

 on either side of it. The hinge-plate is thick, but not 

 furnished with teeth. 



Having regard to the number of natural foes, — 

 apart from man, the most rapacious of them all, — it 

 is not surprising to learn that the progeny — "spat " — 

 of one Oyster may be anything from a few hundred 

 thousands to sixty millions. When discharged by 

 the parent these are furnished with delicate cilia, and 

 by lashing these they float through the water during 

 the first two days. They then settle on some suitable 

 foundation, to which they become permanently attached 

 — or they perish. The character of the weather at 

 this period is of the utmost importance to the future 

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