CHAPTER V 



ADAPTATIONS FOR PROTECTION FROM ENEMIES 



A. The Exoskeleton 



I. THE CLAM — A TYPE OF MOLLUSCA 



To Show the Effect of a Heavy Exoskeleton 



Materials. 



Living clams in aquaria, with enough moist sand to 

 cover the clams, preserved clams, sets of matched clam- 

 shells, a few shells with the huge unbroken, evaporating 

 dishes, hydrochloric acid. 



Definitions. 



Mollusca, a branch of the animal kingdom including 

 those animals with soft, unsegmented bodies, inclosed in 

 two folds of skin known as the mantle. They are often 

 called shellfish as most of the forms have a shell. 



Lamellibranchiata or Pelecypoda, names given to the class 

 of Mollusca to which the clam belongs. The former term 

 refers to the broad, flap-like gills and the latter to the 

 hatchet-like foot. 



Valve, one of two parts of the clamshell. 



Hinge ligament, the elastic structure which fastens the 

 valves together at the dorsal margin. 



Umbones, a pair of elevations near the anterior end of 

 the shell. 



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