CHAPTER X 

 MOLLUSCA 



Shells. — Shells in infinite variety may he picked up 

 on the seashore. These appear in such numbers and 

 have such well-marked characteristics that the study 

 of them is a science in itself. However, in the interest 

 that attaches to collecting and classifying them it should 

 not be forgotten that these shells are merely external 

 skeletons formed for the protection of living animals. 



The Living Animal. — The animal which forms the 

 shell is more important than the shell, and the manifesta- 

 tion of its activities the essential thing. The name mol- 

 lusca is a recognition of this. It comes from the Latin 

 word mollis (soft) and refers to the soft body within 

 the shell. The shell is so wonderfully adapted to the 

 body within that variations in the one are repeated in 

 the other. Characteristics of the living animal may 

 often, therefore, be determined merely from a study of 

 the shells. 



Formation of the Shell. — The shell is formed through 

 the activity of a flap of skin called the mantle which 

 covers the body of the animal. The outer surface of the 

 mantle secretes carbonate of lime, out of which the shell 

 is formed. The shell may split down the middle line 

 forming two pieces, or valves, united by a hinge. It 



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