266 MOLLUSCA 



(a) Number? 



(b) Attachment? 



(c) Use? 



(d) Young. One pair of gills may be much enlarged and 

 filled with young clams, called Glochidia. If present, 

 examine under low power of the microscope. 



(3) The Labial Palpi. These are small leaf-like organs 



anterior to the gills. 



(a) Number? 



(b) Size? 



(c) Use? 



(4) The Siphons. The mantle is modified posteriorly into 



two tubes or siphons. The upper one is the excur- 

 rent and the lower is the incurrent one. A live clam 

 placed in a vessel containing sand covered with water 

 will show the incurrent and the excurrent stream of 

 water, especially if a little coloring-matter is cau- 

 tiously added. Use of these siphons? 



(5) The Body. The soft body with its projecting foot is 



now exposed. 



(a) Shape? 



(b) Size? 



(c) Structure? 



(d) Segmented or unsegmented? 



(6) The Foot. Identify it. 



(a) Shape? 



(b) Size? 



(c) Structure? 



(d) Use? 



(e) How does the clam use it? 



(f) Where must it live to use it? 

 2. The Internal Organs. 



(1) The Digestive Organs. 



(a) The mouth is between the palps. Insert a small 



probe. 

 (1-) Teeth? 

 (2) Tongue? 



(b) The Esophagus leads from the mouth into the 



stomach. 



