16 
INTROBUCTORY LETTER. 
zeal in procuring for us the productions of the middle 
regions of North America. 
In my enumeration of the means at my disposal, I 
have not mentioned the individuals who have furnished 
me with rare specimens, which it would have been very 
difficult for me to obtain, or who have generally contri- 
buted to render my work as complete as possible. I shall 
content myself with citing Professors Van Swinberen of 
Groningen, Vrolik of Amsterdam, Van ber Hoeven, 
and Van ber Boon-Mesch of Leyden, and Dr Hoorn. 
M. Klinkenbero of Utrecht placed in my power the nu- 
merous rarities of his Museum. The Director of the 
Cabinet of Natural History at Vienna gave me permission 
to publish the inedited species contained in that Estab- 
lishment. Dr Thienemann of Dresden gave me about 
twenty figures of serpents, di^awn from the life at Suri- 
nam, by Dr Hering. Above all, I ought to acknowledge 
the liberality of Professors Fremery and Lith be Jeube 
of Utrecht : these philosophers were so obliging as to per- 
mit me to select specimens from the valuable collection 
of Beptiles confided to their care, most of which are na- 
tives of Ceylon, the coast of Guinea, North America, &c. 
I was about to terminate my work, when, at the end of 
a long illness, I had the honour, Sir, to accompany you 
in a journey to Paris, and across a part of Germany. The 
great number of objects which I saw during this journey, 
have obliged me to make several additions to my work ; 
additions, however, which would not have been very im- 
portant, if I had not been permitted to examine, at my 
leisure, objects in themselves rare, or partly new. I owe 
this privilege to the extreme politeness of various philo- 
sophers who are at the head of scientific establishments : 
MM. Duvernoy at Strasburg, and Cretzschmar at Franc- 
fort, were anxious to afford me a free use of the collections 
confided to their care. M. Buppell, whom I have the 
advantage of acknowledging among my friends, has fur- 
nished me with observations on the various reptiles which 
he had an opportunity of examining in his two voyages ; 
and, lastly, the observations of several amateurs of Paris, 
among whom I especially mention Dr Cocteau and M. 
