LAWS OF ANIMAL DISPERSION. Da 37 | 
their dispersion, by heat and cold, except in a se- 
condary and partial way, quadrupeds and birds 
belonging to the same tribes as are found within 
the tropics. would not be present in polar or alpine 
situations. 
There is no portion of our globe, even the most 
desolate, which is not at times visited by certain of 
the higher animals, and also permanently inhabited 
by certain kinds of insects and inferior creatures. 
It thus appears, that besides the lower orders of 
animals being more numerous than the higher 
classes, they are likewise more generally dispersed. 
The resources of the lowest tribes are in all proba- 
bility so obscure and occult as to be not only 
unknown, but even inconceivable by our minds ; 
on the other hand, wherever vegetation attains to 
any tolerable degree of perfection in its various 
forms, there a whole series of animal productions 
presents itself. Ifthe extent of the Flora and Fauna 
of any given country be examined into the above 
result will infallibly be arrived at. 
We may suspect that one primary law on which 
the distribution of animals depends, having a pretty 
general influence and which seems indeed alto- 
getherin unison with the aggregate of our zoological 
knowledge, is the gradual failure in number of in- 
dividuals of a given species as we recede from the 
point which from their comparative plenty there, 
we presume to be their principal seat. ‘Together 
with this numerical failure, we see likewise as 
might easily be conceived, a failure or deterioration 
in size, in qualities, in colour, and in all other 
endowments. To so great an extent is this 
occasionally carried, that naturalists are frequently 
at variance in their decisions on the species, some. 
considering such specimens as deteriorations, others 
viewing them as separate species, or at least as 
formal varieties. It is seen that independently of 
