PREFACE TO THE FIRST EDITION. 



In this I have proceeded, partly by ascending from the inferior to the superior divi- 

 sions, by means of approximation and comparison ; and partly also by descending from 

 the superior to the inferior groups, on the principle of the subordination of characters ; 

 comparing carefully the results of the two methods, verifying one by the other, and 

 always sedulously establishing the correspondence of external and internal structure, 

 which, the one as well as the other, are integral parts of the essence of each animal. 



Such has been my procedure whenever it was necessary and possible to introduce 

 new arrangements ; but I need not observe that, in very many places, the results to 

 which it would have conducted me had already been so satisfactorily obtained, that I 

 had only to follow the track of my predecessors. Notwithstanding which, even in 

 those cases where no alteration was required, I have verified and confirmed, by new 

 observations, what was previously acknowledged, and what I did not adopt until it had 

 been subjected to a rigorous scrutiny. 



The public may form some idea of this mode of examination, from the memoirs on the 

 anatomy of mollusks, which have appeared in the Annates du Museum, and of which I 

 am now preparing a separate and augmented collection. I venture to assure the reader 

 that I have bestowed quite as extensive labour upon the vertebrated animals, the anne- 

 lides, the zoophytes, and on many of the insects and crustaceans. I have not deemed it 

 necessary to publish it with the same detail ; but all my preparations are exposed in 

 the Cabinet of Comparative Anatomy in the Jardin du Roi, and will serve hereafter 

 for my treatise on anatomy. 



Another very considerable labour, but the details of which cannot be so readily 

 authenticated, is the critical examination of species. I have verified all the figures 

 alleged by different authors, and as often as possible referred each to its true species, 

 previously to selecting those which I have indicated : it is entirely from this verifica- 

 tion, and never fiomthe classification of preceding systematists, that I have referred to 

 my sub-genera the species that belong to them. Such is the reason why no astonish- 

 ment should be experienced on finding that such and such a genus of Gmelin is now 

 divided, and distributed even in different classes and still higher divisions ; that nume- 

 rous nominal species are reduced to a single one, and that popular names are very 

 differently applied. There is not one of these changes wluch I am not prepared to 

 'ustify, and of which the reader himself may not obtain the proof, by recurring to the 

 sources which I have indicated. 



In order to lessen his trouble, I have been careful to select for each class a principal 

 author, generally the richest in good original figures ; and I quoted secondary works 

 only where the former are deficient, or where it was useful to establish some com- 

 parison, for the sake of confirming synonymes. 



My subject could have been made to fill many volumes ; but I considered it my 

 duty to condense it, by imagining, abridged means of expression. These I have 

 obtained by graduated generalities. By never repeating for a species that which might 

 be said of an entire suh-genus, nor for a genus what might be applied to a whole 

 order, and so on, we arrive at the greatest economy of words. To this my endeavours 

 have been, above all, particularly directed, inasmuch as it was the principal end of 

 my work. It may be remarked, however, that I have not employed many technical 

 terms, and that I have endeavoured to communicate my ideas without that harbarous 

 array of fictitious words, which, in the works of so many 



