PREFACE TO THE FIRST EDITION. XX1 
a less extended explanation of the subgenera and species, this imperfec- 
tion does not hold in the portion relating to the higher divisions and the 
relative characters, these being every where placed on foundations equally 
solid, the result of researches equally assiduous. 
I have examined, one by one, all the species of which T could procure 
specimens; I have approximated those which merely differed from each 
other in size, colour, or in the number of some parts of little importance, 
and have formed them into what I denominate subgenera. 
At every opportunity I dissected one species at least of each subgenus; 
and if those be excepted to which the scalpel cannot be applied, there 
will then be but very few groups of this degree found in my work, of 
whicn I cannot produce some portion of the organs. 
Having determined the names of the species which I observed, and 
which had been previously either well described or well figured, I placed 
in the same subgenera those I had not seen, but whose exact figures, or 
descriptions, sufficiently precise to leave no doubt remaining as to their 
natural relations, I found in authors; but I have passed over in silence 
that great number of vague indications, on which, in my opinion, natur- 
alists have been too eager to establish species, whose adoption is what 
has mainly contributed to introduce in the catalogue of animals that con- 
fusion which deprives it of so great a portion of its utility. 
I could, every where, have added great numbers of new species, but as 
I could not refer to figures it would in that case have been necessary to 
extend their descriptions beyond my limits; I have preferred, therefore, 
depriving my work of that ornament, and have indicated those only whose 
singular formation gives origin to new subgenera. 
My subgenera, once established on undoubted relations, and composed 
of well ascertained species, nothing remained but to construct this great 
scaffolding of genera, tribes, families, orders, classes and divisions which 
constitute the community of the animal kingdom. 
Here I have proceeded, partly by ascending from the inferior to the 
superior divisions, on the principles of affinity and comparison, and partly 
by descending from the superior to the inferior divisions, on the principle 
of the subordination of characters; carefully comparing the results of 
the two methods, verifying one by the other, and taking care to establish 
always the correspondence of forms, external and internal, both of which 
constitute integral parts of the essence of each animal. 
Such has been my mode of proceeding whenever it was necessary and 
possible to form new arrangements; but I need not observe that, in many 
places, the results to which it would have conducted me had been already 
so satisfactorily obtained, that no other trouble was left to me than that 
of following the track of my predecessors. Even in these cases, how- 
ever, where I had nothing more to do than they had, by new observations 
