HISTORY Of THE OYSTER. 15 



On proceeding further, and dissecting away the 

 upper lobe of the mantle, the two upper bronchia?, 

 and the upper portion of the ovaries carefully, the 

 liver (PI. II. D D D), stomach (PL II. E), intestine 

 (PL II. G), and heart (PL II. F) become apparent. 

 Some difficulty will be found in dissecting away the 

 ovaries, as they are diffused throughout almost every 

 portion of the interior organs. The convolutions that 

 the intestine makes are apparent, with the vent 

 (PL II. H) situated near the right side of the adductor 

 muscle, the liver surrounding the whole of the sto- 

 mach and the principal portion of the central convo- 

 lution of the intestine. Immediately above the ad- 

 ductor (PL LA), the heart (PL II. F) may be observed, 

 by means of which the blood is forced into the fila- 

 ments of the bronchiae, to be impregnated with 

 oxygen. 



This organ has a very different mode of action 

 from our own : it consists of two distinct cavities, 

 one auricle and one ventricle. The latter expels the 

 blood from the heart through the body and the gills 

 or bronchise, from which organs it is received into the 

 auricle and expelled again into the ventricle, thus 

 completing the circuit of the arteries and veins. 



The nervous system in the Oyster is of course low : 

 there being no distinct brain, the principal nervous 

 centre or ganglion is situated on the inner side of 

 the adductor muscle (PL III. fig. 1 , A), which com- 



