476 



ZOOLOGY. 



whole or in part, presenting superiorly a hinge, provided with 

 an elastic ligament, by the play of which the valves are 

 opened whenever the muscles, extending from one to the other, 



m' a i f v' 



Fig. 458. Anatomy of the Oyster.* 



cease to act. The viscera are collected into a small mass, 

 under the dorsal part of the mantle, and the ventral portion of 

 the body is generally prolonged so as to form a fleshy foot, 

 having some analogy with the gasteropodes, but not so well 



Fig. 459. Telline (Tellina). 



formed for locomotion. Sometimes it is the inner surface of 

 the mantle, as in the terebratulae, which takes the place of 

 the respiratory organ, and for this purpose shows a highly 



* r, one of the valves of the shell ; c', the hinge ; w, one of the lobes of the 

 mantle ; *', portion of the other lobe, laid upwards ; c, muscles of the shell ; 

 br, the gills; b, the mouth; I, labial tentacles ;/, the liver ; , the intestine ; 

 a, the anus ; eo, the heart. 



