DISTRIBUTION OF OPHIDIANS. 237 



central America, consisting of a narrow tongue of land 

 uniting those two continents, and the adjacent islands, 

 sustain a great number of animals, which have one or 

 other of the two continents as their original country. Some 

 species of animals, however, are common to both Ameri- 

 cas. Others abounding in North America are found 

 under the same parallels of latitude in South America, 

 where they also form climatal varieties. A great number 

 of species inhabiting the southern continent are also found 

 in Mexico, and the Antilles ; while there are others, com- 

 mon in South America, that are diffused in North Ameri- 

 ca, over Florida and Louisiana, where they often form 

 climatal varieties. Local differences are sometimes even 

 remarked between animals of countries less separated than 

 those just mentioned ; for example, Brazil and Surinam, 

 or Guyana in general. Lastly, the animals of the regions 

 situated on the western slopes of the Cordilleras, often 

 differ specifically from those of Brazil ; but certain species 

 are the same in both regions, or at most only exhibit 

 slight variations. South America produces a great num- 

 ber of monkeys, of which no race has been yet observed in 

 North America ; and these monkeys, the same species of 

 which is sometimes found over an extent of country em- 

 bracing more than 20° of latitude, must necessarily pre- 

 sent, in places so distant, differences more or less sensible, 

 chiefly arising from the influence of climate.* A very great 

 number of other animals of South America have not 

 hitherto been observed in the northern peninsula of the 

 New Continent, such as the Llama, which may be termed 



* It is stated as a fact, that the Monkeys of Paraguay cast their hair 

 at certain seasons of the year, to be reinvested with a denser fur, a 

 species of winter robe, which does not take place with individuals of 

 the same species living under the equator. Add to this, first the al- 

 most incredible changes which some monkeys undergo from age, and 

 afterwards the differences which usually exist in these animals between 

 the sexes, and we may conceive the difficulties in the way of those who 

 occupy themselves with the study of those animals. I cannot sufficient- 

 ly recommend to cabinet-naturalists the perusal of the precious works 

 bequeathed to us by the late Rexgger, whose observations I have often 

 had occasion to verify, from the numerous materials afforded by the 

 Museum of the Low Countries. 



