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. Al] 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 
