54 MOLLUSCA. 



sary consequences of an artificial system, and they become 

 more obvious in proportion as we descend in the scale of 

 being. 



The examination of shells, according to this method, may 

 be viewed as the study of the osteology of the mollusca. It 

 has not for its object the investigation of living matter, but 

 of dry bones. Nor has it any of those advantages which 

 result from the study of the osteology of the vertebral ani- 

 mals. A knowledge of the bones of these animals enables 

 us to ascertain many of their primary functions, the nature 

 and extent of their powers of motion, and even the food on 

 which they subsist. But our knowledge of shells does not 

 enable us to say, whether the animal can crawl or swim; 

 whether it feeds on plants or animals. The reason is obvi- 

 ous. All the muscles inserted upon the shell are either 

 mere organs of adhesion, or destined to open and shut the 

 valves. None of those muscles connected with any of the 

 primary organs have any connection with the shell. That 

 the shell furnishes several most important characters, we 

 readily grant ; but we are here reasoning against the pro- 

 priety of attending to the shell, to the exclusion of the animal, 

 and, to this extent, our reasoning appears to be conclusive. 



We are aware, that, in the other departments of natural 

 history, the appearances which the external parts of an ani- 

 mal exhibit are constantly employed in the construction of 

 orders and genera, and all the intermediate divisions. Thus, 

 for example, the bill, feet, and feathers of birds, furnish the 

 characters by which they are arranged in the system. Here, 

 however, it must be observed, that the combined informa- 

 tion yielded by these parts, makes us acquainted with the 

 habits and organization of a bird. By means of these we 

 can judge, and with certainty, not merely of its internal 



