240 ELEMENTARY ZOOLOGY 



TECHNICAL NOTE. Specimens which are to be dissected should 

 be killed by dropping them for a few seconds into warm water, when 

 the muscles will relax enough so that a chip may be thrust between 

 the valves. If specimens are to be kept for some time before dis- 

 secting they should be preserved in alcohol or 4^ formalin. In a 

 dead specimen carefully remove the left valve. This is accomplished 

 by slipping in a thin knife-blade close to the inner edge of the left 

 valve and carefully cutting the two large adductor muscles which 

 bind the valves together. The dissection should be made under 

 water. 



Before the removal of the valve, as just described, 

 notice a portion of the mantle adhering to the Inner face 

 of the valve, along a line of attachment indicated by a 

 crease. This is the pallial line. After the left valve has 

 been removed, the mantle being carefully separated from 

 it, note the large conical projections from the valves, the 

 hinge teeth, which fit into each other. Note the large 

 muscle impression just in front of the hinge-teeth ; this is 

 the point of attachment of the anterior addtictor muscle, 

 while just behind and adjoining it is the impression of the 

 anterior retractor muscle. Note posterior to the adductor 

 and below the retractor a small impression which affords 

 attachment for the protractor muscles of the foot. At 

 the other end of the valve, note the large impression of the 

 posterior adductor muscle with the impression of the small 

 posterior retractor muscle just above it. 



TECHNICAL NOTE. Lift back the left mantle-lobe, thus exposing 

 the body parts underneath. 



Note the projecting muscular foot, the movements of 

 which are governed by the retractor and protractor 

 muscles attached to the impressions just mentioned. 

 Note a pair of flattened plate-like structures composed of 

 thin, ribbed, membranous folds. These are the gills. 

 Note just beneath the anterior adductor muscle a small 

 opening leading into the soft visceral mass of the body. 

 This is the mouth. Note near the mouth two pairs of 

 olate-like structures much smaller than the gills. These 



