Mollusca. 55 



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Position of the Clam. Drop several clams into the water and 

 note carefully the place and position of each. Watch them as 

 closely as possible to see if they change their place or position, 

 and if so, learn how this is done. 



Locomotion. Watch clams that have established themselves in 

 their natural position, to find out how they travel. Do they 

 leave a track? If so, of what sort is it? Is the motion slow or 

 rapid? Is it at a uniform rate, or irregular? Quickly pull up a 

 clam that is moving and note the projecting foot. Place a clam 

 close to the side of a glass aquarium ; the foot may be protruded 

 so close to the glass as to be seen. Why do clams travel? Can 

 a clam crawl on a hard surface? 



Water Currents. Note that a clam, when established in a 

 natural position and left undisturbed, has the shell slightly open. 

 Near the upper edge of the more exposed end look for two 

 elliptical holes ; these are the siphons. Watch to see if there is any 

 evidence of currents through these holes. Reduce the amount of 

 water so that it is about half an inch deep over the siphons of a large 

 clam. Look closely at the surface of the water over the siphons for 

 evidence of water currents. Take a slender glass tube, dip one 

 end in ink, place a finger over the upper end of the tube and lift 

 out a little ink. Carefully introduce a drop of this above the 

 siphon opening. The currents may also be revealed by a little mud, 

 but care should be taken not to drop coarse mud or sand on the 

 siphons. What happens when the margins of the siphons are 

 touched? Pull up a clam that is in "full blast," watching closely 

 the siphons. Describe what you observe. 



Senses of the Clam. Test in various ways the senses of the clam. 

 Touch it lightly and heavily ; jar the floor near the aquarium. 

 Throw strong light (without heat) upon it. Try heat without light. 

 Test for all the senses you think a clam may possess. 



Protection of the Clam. Note again the changes that take place 

 when an active clam is taken from the water. Now try to open 

 the shell with the hands alone. Why does the clam have such a 



