100 GRADATION AMONG ANIMALS. 
animals are not scattered over the surface of our 
globe at random, but that they are associated to- 
gether in what are called fauna, and that these 
faune have their homes within certain districts 
called by naturalists zodlogical provinces. The 
limits of these provinces are absolutely fixed, in 
the ocean as well as on the land, by certain phys- 
ical conditions connected with climate, with alti- 
tude, with the pressure of the atmosphere, the 
weight of the water, etc.; and this is true even 
for animals of migratory habits, for all such mi- 
grations are periodical, and have boundaries as 
definite and impassable as those that limit the per- 
manent homes of animals. There is a certain 
series established by the relations between differ- 
ent kinds of -animals, as thus distributed over the 
globe, agreeing with the gradation in their rank, 
their growth, and their succession in time ;— the 
law which distributes animals in adjoining faune, 
and in accordance both with their relative superi- 
ority or inferiority, and with the physical condi- 
tions essential to their existence, being the same 
as that which controls their structural relations, 
their embryological development, and their suc- 
cession in time. 
What, then, does this correspondence between 
the Series of Rank, the Series of Growth, the 
Series of Time, and the Series of Geographi- 
cal Distribution in the life of animals teach us? 
