424 



MOLLL'SCA: ACEPIFALA. 



Mussels, etc., move by protruding the foot and then con- 

 tracting it; and others, as t'arrft'wn, Trigoni.a, etc., have 

 the foot so bent that they can make short leaps. The 



FIG. 629. 



FIG. 628 



Thorny Oyster, Spondylus amcularis. 



Mt/liliis edulis, L. Reduced 

 Botli shores of the Atlantic 



Pentens (Fig. fi'22), liowever, move by opening and shutting 

 the valves of the shell, and ejecting the water caught be- 

 tween the valves, and thus forcing themselves along. 



And it should be added here, that some kinds are con- 

 stantly fixed in their adult state, the Sea-Mussel and 

 Pinna being attached by threads, which they spin, and 

 which are called a byssus (Fig. 629) ; and the Oyster and 

 Spondylus being attached by leafy expansions, or by spines 

 of their shell (Fig. 62S). 



Bivalves reproduce by means of eggs, and are exceed- 

 ingly prolific, some kinds, as the Mussels and Oysters, 



FIG. 630. 



FIG. 631. 



Gastrocha>na 



Lam. Gahvay. 



Aspergillum vaginijerum, Lam. Reduced. Rsd Sea. 



