CHAPTER XVI 



phylum x.— mollusca 

 Laboratory Exercises 



279. The Clam (Mya) 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 labora- 

 tory and placed in a tub of water with a few inches of sand at 

 the bottom, where something of the physiology may be studied 

 with profit. If they cannot be collected when needed for study, 

 they should be well hardened and covered with the preservative 

 fluid in which they are to be 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 you 

 think all your specimens belong to the same species ? 



In nature or 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, and the position of the animal during motion? 

 Note the trail. Determine anterior and posterior ends, right 

 and left sides, dorsal and ventral surfaces. How is this done ? 

 To what extent can the soft parts protrude from the shell? 

 Note briefly, for later reference, the position of all visible struc- 

 tures. How widely does the shell open during life? 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 solu- 

 tion. Devise experiments to test whether the animal shows 



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