CHAPTER XVI. 

 PHYLUM VI. MOLLUSCA. 



LABORATORY EXERCISES. 



273. The Clam (My a) or Mussel (Anodonta, Unio). 

 Either the marine or the fresh-water type will serve. The 

 latter are to be found in almost all our streams and small 

 lakes. They may be obtained with a long handled rake from 

 the shore or from a boat. They often occur partly buried in 

 the sand or mud. If kept in water they may be transported 

 to the laboratory and placed in a tub of water with a few 

 inches of sand at the bottom, where something of the physi- 

 ology may be studied with profit. If they cannot be collected 

 when needed for study, care should be taken to supply plenty 

 of the preservative fluid in which they are kept. 



i. The Living Animal. What facts were observed, in col- 

 lecting the material, concerning their haunts, their abundance 

 in different localities, their range in size, etc. ? Are there any 

 efforts at active feeding, as far as you have seen ? Do all your 

 specimens belong to the same species? 



From the specimens in the tub make out the following 

 points : 



Has the animal power of voluntary motion? If so, what of 

 its rate, manner, the position of the animal during motion? 

 How is the animal supported in this position? Determine an- 

 terior and posterior ends, right and left sides, dorsal and 

 ventral surfaces. To what extent can the soft parts protrude 

 from the shell? Note briefly, for later reference, the position 

 of all visible structures. How widely does the shell open 

 during life? Note the trail. With a pipette place a drop of 

 some colored but harmless fluid (carmine in water) near the 

 fringes of the posterior end, and note the results. Vary by 

 introducing salt, sugar, and acid in the solution. Devise 



234 



