356 ZOOLOGY 



XII. FRESH-WATER CLAM (Anodonta or Unio} 



Venus may be substituted for these ; and Mya is a favorable object 

 for this study. Anodonta or Unio may be obtained from most 

 streams and ponds at any time of the year except midwinter. This 

 exercise will therefore be best taken in the spring or autumn. To 

 prepare animals for the study of the soft parts, place them in hot 

 water (60 C.) for a few minutes; the valves will then open so that 

 the muscles can be cut where they join the shell. 



DRAWINGS 



1. Exterior of left valve, showing lines of growth, beak, and margin. 

 Natural size. 



2. Interior of right valve ; name some of the more important parts, 

 such as margin, scar of mantle, scars of adductor muscles, and retrac- 

 tor of foot, hinge. Natural size. 



3. Bit of fractured edge of burnt shell, to show layers, x 5. 



4. Remove the left valve from the killed animal and draw the exter- 

 nal form of the soft parts from the left side, x 2. 



5. Laying back the mantle, draw in place gills (showing surface 

 structure), body, foot, and labial palps; mark anterior, posterior, 

 dorsal, and ventral surfaces of the body, x 2. 



6. Draw an imaginary cross-section made through the middle of the 

 body. 



QUESTIONS TO BE ANSWERED BY INFERENCE FROM STRUCTURE 



1. How does the shell grow? 



2. How does the animal close its shell ; how open it? 



3. How does the animal gain its food ? 



OBSERVATIONS ON THE LIVING ANIMAL 



Every student should be provided with the following : (1) vial con- 

 taining finely powdered carmine in water; (2) vial of carmine in 5% 

 acetic acid; (3) carmine in 5% sulphuric acid ; (4) carmine in sugar 

 solution ; (5) pipette ; (6) 4-inch battery jar half full of water. 



1. Notice in a living individual in the aquarium the movements of 

 the mantle, especially at the posterior end. 



