CATECHISM OF CONCHOL.OGY. 1 



Q. In what respect do they differ fromeach 

 other ? 



A. A considerable difference is observable, 

 according to the different situations which they 

 inhabit : those which are not oceanic, being far 

 more fragile and transparent than such as have 

 to endure the rough beating of a boisterous sea. 

 Many of those which inhabit still ponds and 

 muddy ditches are scarcely able to resist the 

 slightest pressure. 



Q. How are the shells formed ? 



A. It appears from the accurate investigations 

 of Leuwenhoeck and Reaumur, that an infant 

 shell-fish is uniformly furnished with a testaceous 

 coating, which gradually increases by means of 

 a viscous exudation from the aperture or hinge 

 round the circumference of each valve, and forms 

 a coat of mail adapted to the exigencies, and 

 proportioned to the shape of the wearer. 



Q. This is very extraordinary. But why is it 

 that this strong exudation condenses only on 

 those parts where it is essential to the welfare of 

 the animal ? 



A. Here investigation ends; the microscope 



