46 FIRST BOOK OF ZOOLOGY. 



the smaller and flat valve, which is the right one. To ex- 

 amine it properly, the specimen must be placed in a deep 

 saucer filled with water, so as to cover it. A number of 

 rinsings will remove the mucus with which the oyster is 

 covered, and this will render the specimen in better con- 

 dition to examine. In placing it under water in this way, 

 the membranes float apart, and can be more readily 

 studied. 



45. The adductor muscle is near the middle of the animal. 

 It is composed of two elements, one half being of a glistening 

 white, and the other half being grayish. Immediately ad- 

 joining the grayish portion of the muscle, a translucent space 

 is seen, and this space contains the heart, composed of a body 

 constricted in the centre, as if a tube had been tied in the 

 middle by a string. This is the heart proper, and in speci- 

 mens freshly opened the heart may be seen to slowly pulsate, 

 or beat. 



By raising the mantle, the gills will be seen as delicate, 

 leaf-like membranes. 



At the smaller end of the oyster, and that portion which 

 comes next to the beak or hinge, the mouth will be found 

 having on each side two delicate lappets, which are called the 

 palpi. It will be difficult to find the mouth, and some pa- 

 tience will be demanded in lifting the mantle and following 

 up between the palpi to where the mouth is. 



The dark region just back of the mouth contains the 

 stomach and liver ; the dark or blackish portion, showing so 

 conspicuously in cooked specimens, being the liver. 



