142 MOLLUSKS 



auricle, somewhat conical, with the small end at the heart. 

 Do you find its opening into the heart ? The blood is gath- 

 ered into the auricle from the gills, thence to the ventricle, 

 where it is received and sent out mainly through an artery 

 leading forward toward the foot, from which it is distributed 

 through the body and returned to the gills. Has any other 

 animal you have studied a circulation like this? Draw dia- 

 gram of the circulatory system as it appears to you. Remove 

 the animal from the shell. Observe the large muscles at 

 anterior and posterior ends, the adductors, which hold the 

 valves of the shell together. Do you find other muscles at 

 the anterior end attached to the shell back of the anterior 

 muscle? These are the retractor muscles. What do they_ 

 retract ? Of what value are they in the movement of the 

 foot? Turn the animal over, fold back the mantle, and 

 make drawing as now exposed, showing and naming all the 

 parts studied. 



(2) Using an alcoholic specimen, find the mouth, and 

 insert a bristle into it, and follow with the scalpel, cutting 

 from the outside. The alimentary canal is rather crooked, 

 but may be followed if care is used. Do you find the Hverf 

 The kidneys? Follow the intestine through the heart and 

 find where it empties into the siphon. Which siphon does 

 it empty into? Draw digestive system. 



(3) The nervous system is somewhat difficult to trace, 

 but the general plan may be worked out. It is best to use 

 alcoholic specimens for this work. The cerebral ganglia 

 may be found at the base of and between the labial palpi. 

 These nerves go to difl^erent parts of the body, and with 

 care nerve cords may be traced downward toward the foot 

 to a larger group of pedal ganglia located where the foot 



