XIV PREFACE TO THE FIRST EDITION. 
the Annulata, the Radiata, and many of the Insects and Crus- 
tacea, is equally extensive. I have not deemed it necess- 
ary to publish it with the same detail; but all my prepara- 
tions are exposed in the Cabinet of Comparative Anatomy in 
the Jardin du Roi, and will serve hereafter for my Treatise 
on Anatomy. 
Another work of considerable labour, but whose proofs 
cannot be made so authentic, is the critical examination of 
species. I examined and verified all the figures adduced by 
authors, and as often as possible referred each to its true spe- 
cies, before making a choice of those I have pointed out; it is 
from this verification alone, and never from the classification 
of preceding methodists, that I have referred to my sub- 
genera the species that belong to them. Such is the reason, 
why no astonishment should be experienced on finding that 
such or such a genus of Gmelin is now divided and distributed 
even in different classes and divisions; that numerous nominal 
species are reduced to a single one, and that vulgar names are 
very differently applied. 
There is not a single one of these changes that I am not 
prepared to justify, or of which the reader himself may not 
obtain the proof by recurring to the sources I have indicated. 
In order to diminish his trouble, I have been careful to se- 
lect for each class a principal author, generally the richest in 
good original figures, and I quote secondary works only in 
those cases in which the former are silent, or where it was 
useful to establish some comparison, for the sake of confirm- 
ing 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 publication. I have obtained these by gra- 
duated generalities; by never repeating for a species what 
could be said of a whole subgenus, nor for a genus what might 
be applied to an entire order, and so on, we arrive at the 
greatest possible economy of words. ‘To this my endeavours 
have been, above all, particularly directed, inasmuch as this 
was the principal end of my work. It may be observed, 
