90 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.’ 
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, z.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 
pelecypods 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, 7.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; 
1The 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. 
