202 THE OYSTER. 



anterior chamber, (A 1 ,) and the circulation again repeats the round 

 from the ventricle (/*') into the body and mantle, thence to the 

 gills, and finally back to the auricle. 



The digestive system consists of a tube, of varying thickness, 

 which doubles upon itself twice in its course from mouth (m) 

 to vent (an). From the mouth (m) the stomach (st, st 1 ) broad- 

 ens backwards, without the intervention of a throat, in the mass 

 of brown liver (/, I 1 } which surrounds it, and then slightly nar- 

 rowing, it passes in a direct line, below the heart and along the 

 lower side of the muscle, (ms,) almost to the posterior end of 

 the gills. There it abruptly narrows into an intestine, (in,) which, 

 making a sudden bend, (st'*,) passes pretty closely along the right 

 side of the stomach, back to the liver, (I, I 1 ,) into which it enters 

 and passes along near its right side, (at in 1 ,) and then across its 

 forward end, nearly over the mouth, (m,) and down the left side, 

 and then, making a long curve, rises again toward the upper side 

 of the liver, and, passing out of it, bridges over the space in 

 which the heart lies, and comes to a termination (an) on the 

 upper side of the adductor muscle, (ms,) and to the left of the 

 line along which the stomach passes. 



The nervous system consists principally of two widely distant 

 masses or groups of ganglions. One of them lies across the 

 upper lip of the mouth, and the other below the great muscle 

 near the first bend of the intestine; and the two are connected 

 with each other by delicate nervous threads which pass along on 

 each side of the body. The anterior mass is called the " cerebral 

 ganglion," or brain, and the posterior one the " branchial gan- 

 glion," on account of its supplying large nerves to the gills, as 

 well as to other neighboring parts. 



The reproductive organ (ov) lies just behind the liver and 

 under the stomach. It is an irregular mass, which, with the liver 

 and certain other smaller bodies of an undetermined nature, form? 

 a basis on which the stomach and intestine lie, or pass through. 



These organs, and the great double muscle, form the bulk of 

 the body, upon which the right and left mantle is laid, and from 

 which the four gills hang in long, parallel, unequal strips. Every- 



