XVI JNTRODUCTION. 



tends to prove that shells increase by a perfect juxta- 

 position of calcareous beds, united by a viscous 

 cement, and formed successively from the interior 

 of the shell, as the animal advances in growth. 

 These beds may be made very evident, by heating 

 an oyster-shell in the fire, without totally destroying 

 its organization. It may then be easily separated 

 into the different beds (or leaves) which form its 

 substance, and the mechanism of the shell com- 

 pletely exposed, 



