DISTKIBUTION 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 Renoger, whose observations I have often 
had occasion to verify, from the numerous materials afforded by the 
Museum of the Low Countries. 
