INTRODUCTION. 107 
This distribution is sufficiently correct, in a gene- 
ral point of view, to merit consideration; and the 
modifications which can be pointed out in the habi- 
iat may well be ascribed to the migrations of man, 
the necessity of administering to his wants and his 
pleasures, and therefore to his particular care ; 
which, after all, never enabled him to carry out his 
desires beyond the few degrees of cold and heat, 
one way or the other. If, then, by their conforma- 
tion, these animals were not invincibly debarred the 
faculty of breeding together and producing prolific 
lines of descent, we would find the great variety of 
races of dogs now existing completely accounted 
for by the demoralization they have suffered from 
slavery. For although the laws which bind organized 
beings within the prescribed limits of given ana- 
tomical and external consimilarities, still that power 
whence these laws emanated, has also shown itself 
in their exceptions. Exceptions that would in all 
probability be much more numerous, if our know- 
ledge was more extended and accurate. Some have 
been already pointed out, others are known to exist 
in other classes of animals, as in birds organized on 
a different but not an inferior plan, such as the hy- 
brid between different species of ducks, as well as 
finches, whose offspring are equally prolific and 
continuous. 
To the objection that in this manner the difficulty 
of the question is avoided but not overcome, we 
answer, that the foregoing arguments tend at least 
to support the general inference, and that we do not 
