84 INVERTEBRATE ZOOLOGY 



Kill the animal by immersing it for a few minutes in hot 

 water (70 C.). As the shell is kept closed by the contraction of 

 the two muscles which pass between its valves, it will gape open 

 as soon as the animal is dead and the muscles are relaxed. It is 

 the elasticity of the hinge ligament which causes it to open. 1 



Examine the animal as it lies in the shell. It will be 

 seen that the inner surface of each valve is covered with a 

 soft, slimy membrane, the lower edge of which is parallel to 

 the edge of the shell. This is the mantle; it is a double 

 fold of the dorsal integument of the body, one side of the 

 body being covered by either fold. The mantle is the matrix 

 of the shell, i.e., it secretes the shell. Its lower edge is pro- 

 vided with muscle fibers and can be extended beyond the edge 

 of the shell ; it also possesses sensory functions ; in some 

 lamellibranchs eyes are situated along the mantle's edge. 



Observe the large, soft visceral mass hanging between the two 

 lobes of the mantle ; it contains the viscera of the animal. On 

 the lower side of the visceral mass, i.e., toward the gape of the 

 shell, is the muscular foot, which can be extended below the edge 

 of the shell and is the organ of locomotion. Observe the 

 two leaf-like gills on each side of the visceral mass and foot; 

 also the two large adductor muscles, one in front of and the other 

 behind the visceral mass, which pass from one valve of the 

 shell to the other and serve to close them. 



Pass a knife between the mantle and the left shell and sepa- 

 rate them from each other. Cut the two muscles close to the 

 shell ; cut the elastic hinge ligament and remove the left shell. 



Study the inner surface of the shell. Note the two large scars 

 marking the surfaces of attachment of the adductor muscles; 



1 The shell may also be opened by inserting some sharp, wedge-shaped 

 instrument between its valves. The valves are thus pressed apart far enough 

 to admit the blade of a scalpel, by means of which the adductor muscles should 

 be cut close to the left valve of the shell. The hinge ligament should then be 

 cut and the left valve be removed. 



