ssfetet. 



Pearl divers. 



CHAPTER IX 



MOLLUSCS 



The Fresh-water Mussel 



Suggestions. — The mussel is usually easy to procure from 

 streams and lakes by raking or dredging. In cities the hard- 

 shelled clam, or quahog, is for sale at the markets, and the follow- 

 ing descriptions apply to the anodon, unio, or quahog, with 

 slight changes in regard to the siphons. Mussels can be kept 

 alive for a long time in a tub with sand in the bottom. Pairs of 

 shells should be at hand for study. 



External Features. — The shell is an elongated oval, 

 broader and blunter at one end (Fig. 188). Why does 

 the animal close its shell ? Does it open the shell ? 

 Why ? Does it thrust the foot forward and pull up to it, 

 or thrust the foot back and push ? (Mussels and clams 

 have no bones.) Does it go with the blunt end or the more 

 tapering end of the shell forward? (Fig. 188.) Can a 

 mussel swim ? Why, or why not ? 



97 



