520 



ZOOLOGY. 



side a large fold, covering all the other part of the animal 

 (Pig. 544), and sometimes even is so united to its fellow of 

 the other side, as to leave openings only behind and before, 

 and to form two long tubes for the water necessary for respi- 



m' a i f v 



Fig. 544. Anatomy of the Oyster.* 



ration. A shell, composed of two valves, covers this mantle 

 in 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, 



Fig. 545. Tellina. 



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

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



* v, one of the valves of the shell ; v', the hinge; m, one of the lobes of the 

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

 br, the gills ; b, the mouth ; I, labial tentacles; f, the liver ; i t the intestine ; 

 a, the anus ; co, the heart. 



