MOLLUSCA. 59 
arriving at its name and history. This defect, however, 
is partly remedied when we can call to our aid the charac- 
ters furnished by the shell. 
Another objection against this method arises from the well 
known difficulties attending the preservation of the soft parts 
of molluscous animals. Todry these, destroys their form and 
texture ; to inject them is impracticable; and when put 
into spirits of wine, they generally appear a shrivelled mass. 
But the coverings of these animals are durable, and, since 
they form a part of the animal; since they are produced at 
first along with it, increase by the addition of new matter 
from its body, and continue attached to it for life ; we must 
condemn any classification from which the shell is excluded. 
From these remarks, it will be obvious, that we consider 
the mixed system as the most natural and the most useful. 
It possesses all the advantages to which the other systems 
lay claim, while it is free from their defects. It withdraws 
part of our attention from the shell, because it is destitute 
of peculiar vessels, and possesses no vital energy, to fix it 
on those organs of the animal which are subservient to its 
existence. It leads us to examine the whole animal, instead 
of certain parts of it merely, and has a tendency to excite 
us to become acquainted with the manners of a tribe, from 
which, imperfect and artificial systems have hitherto with- 
drawn our attention. ? 
VALUE OF THE CHARACTERS EMPLOYED. 
It is of the utmost importance in the formation of any ar- 
rangement of natural bodies, to have an exact idea of the 
relative value of the characters used, and of their true sub- 
ordination. This is a subject of vast moment, and too little 
