CLASSES OF THE MOLLUSCA. 



to see ; and here, as in his botany, employed an artificial, in pre- 

 ference to a natural method. 



The systematic arrangement of natural objects ought not, 

 however, to be guided by convenience, nor " framed merely for 

 the purposes of easy remembrance and communication." The 

 true method must be suggested by the objects themselves, by 

 their qualities and relations ; it may not be easy to learn, it 

 may require perpetual modification and adjustment, but inas- 

 much as it represents the existing state of knowledge it will aid 

 in the UNDERSTANDING of the subject, whereas a " dead and 

 arbitrary arrangement" is a perpetual bar to advancement, " con- 

 taining in itself no principle of progression." (Coleridge.) 



Fig. 7. A Bivalve.* 



Fig. 8. A Tunicavy.^ 



Mya truncata, L. . From Forbes and Hanley. 



t Ascidia merttula, Mull. Ideal representation; from a specimen dredsred 

 by Mr. Bowerbank, off Tenby. 



B 3 



