INTRODUCTORY LETTER. 
5 
in fact merely species, &c. To what results must such 
views lead ! 
The critical examination of the works of my predeces- 
sors has cost me much labour : it was necessarily severe. 
I have been so ; but I have also been impartial. I pro- 
fess not to understand how several of these works, so dif- 
ficult to consult, could be useful to the traveller, who, in 
his quality of general describer, should be able rapidly to 
familiarize himself with the nature of existences, as a guide 
to his observations. A book is usually, for the philoso- 
pher living in a country town, his sole means of studying 
the exotic productions of nature ; in a word, books also 
stand him in the stead of collections. My book is only 
intended to answer this end, or that of communicating my 
observations to the public, or to those who have not the 
power of making such for themselves. 
You can conceive, sir, that I have encountered great 
difficulties in the course of my work— difficulties which 
have their origin either in the nature of the subject, or in 
the mode in which the science has hitherto been cultivated. 
The first object of my researches was the rigorous deter- 
mination of species. To attain this end, I was obliged to 
frame a history of each of them, to, study chronologically 
its synonymy, to make commentaries on iconographic 
works, in order to prove, by means of the comparison of 
figures and descriptions, the identity of innumerable no- 
minal species, with some of those which I know to exist. 
It was principally in devoting myself to this ungracious 
and fastidious labour, that it was necessary to employ the 
most rigid criticism. I shall not now enter into further 
details to discuss the question, whether there exist certain 
species in nature or not, or if it be necessary to acknow- 
ledge the existence of races, &c. ; I shall confine myself 
to a justification of my ideas, when they contradict those 
of my predecessors. 
I purpose to admit into my work no species but what 
is known in a precise manner. In submitting the species 
received into the methodical catalogue of existences to a 
rigorous examination, a great number will be found of 
uncertain origin ; some are established from old specimens 
