PREFACE TO THE FIRST EDITION. 5 
111 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 Annales 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 from the 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 which I am not prepared to 
justify, 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 sub-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 w^ork. It may be remarked, however, that I have not employed many technical 
terms, and that I have endeavoured to communicate my ideas without that barbarous 
array of fictitious words, which, in the w'orks of so many modern naturalists, prove 
