FORMATION OF SHELLS OF ANIMALS, 
fe. 
Tue observations about to be made upon the mode of 
formation of organic structures, rest upon the fact, that, 
by a proper employment of chemical and mechanical 
means, and by an exact adjustment of the conditions 
under which they act, calcareous bodies, identical in struc- 
ture and similar in composition to the elementary forms 
of the structures above mentioned, can be artificially pro- 
duced. It will therefore be necessary, first, to describe 
minutely the artificial process for obtaining these bodies, 
and to explain the manner.in which the physical and 
chemical agencies therein engaged act in producing them ; 
and, secondly, to show that, wherever natural products are 
found identical in structure with the artificial ones, the 
existence of physical and chemical conditions, similar to 
those associated in the artificial process, can be demon- 
strated. : 
Hence the subjects announced in the title fall naturally 
under two heads: one, embracing all such considerations 
as are strictly physical, and admitting of experimental 
demonstration, without any possible interference from 
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