36 STUDIES OF ANIMAL TYPES 



the valves. Observe how closely they fit together. Re- 

 move the uppermost valve. 



(Further dissection is best done under water. The water will 

 cause the different parts to float separate from each other so that 

 they may be easily distinguished.) 



Note that the mantle lines the inside of both valves and 

 completely surrounds the body. Observe the two siphons 

 at the posterior end of the shell. Note that they are formed 

 by the mantle. The lower one is the inhalent and the upper 

 one the exhalent siphon. Note at each end of the shell a 

 very large thick muscle that was cut by the scalpel. The 

 muscle at the posterior end is the posterior adductor muscle. 

 The one at the anterior end is the anterior adductor muscle. 

 They hold the valves tightly shut. Observe beside each 

 one smaller oblique muscles, the anterior and posterior 

 retractor muscles, respectively. 



Turn back the half of the mantle torn from the valve. The 

 space inclosed by the two lobes of the mantle is called the 

 mantle cavity. In this mantle cavity, as the lobe is turned 

 back, note the two pairs of thin, ribbed gills, a pair on each 

 side of the body. Note the soft white abdomen between 

 them. The water, laden with food, is taken through the 

 inhalent siphon into the mantle cavity. The food is passed 

 into the mouth, but the water passes through the gills, 

 aerating the blood, and finally goes out through the exhalent 

 siphon. 



Loosen the mantle and body on the dorsal side very 

 carefully and pull them a little from the remaining valve. 

 This will bring the dorsal side of the body into view. On 

 the middle line of the dorsal side cut carefully through the 

 mantle and the other delicate tissue until a cavity is laid 



