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. To dry 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 



