PLAN OF THE WORK. 



(3.) Under all these circumstances, we must therefore 

 treat the molluscous groups with great brevity : the lead- 

 ing divisions, indeed, of the whole will be briefly stated, 

 sufficient to guide the researches of those who may be 

 disposed to adopt our views of natural arrangement, and 

 to analyse their contents ; but this will be entirely 

 subordinate to the primary intention of this volume, 

 which, it will be seen, is almost exclusively confined to 

 the Testacea. Limited as is our space, we shall 

 endeavour to fill it in that way which promises to be 

 of the greatest permanent, as well as practical, advantage 

 to science. The arrangement of one class of the Mol~ 

 lusca, founded upon analysis, is obviously more valu- 

 able than a theoretical digest of the whole. We are 

 seeking to place zoology upon a new basis. To discover 

 and develope, as far as in us lies, the fundamental prin- 

 ciples of the natural system ; and to exhibit its compo- 

 nent parts — not as detached portions, as if each had 

 its own set of laws and its own little system of arrange- 

 ment, but — as a vast and connected whole, throughout 

 which the utmost harmony and the most perfect unity 

 of plan pervades. To do this, however, with any 

 degree of success, requires a fulness of detail, insepa- 

 rably connected with the comprehensiveness of the 

 subject, and the novelty of the design. It is due, not 

 only to the scientific public, but to the labours of those 

 great men whose opinions now reign paramount, that 

 the systems now in use should not be lightly set 

 aside. Hence a variety of details, unnecessary under 

 other circumstances, becomes absolutely essential in 

 these. Now, of the three classes of molluscous animals, 

 the Testacea, or shell-fish, is that which possesses the 

 greatest degree of popular, and even of scientific, in- 

 terest. Their beautiful shelly habitations form some of 

 the most interesting objects in our public museums 

 and private collections. And although we should not 

 consider ourselves bound to make this the only reason 

 for a neglect of the other classes of the Mollusca, yet, 

 •nnder existing circumstances, we shall so far concede to 



