ls the
geographical distribution of animals over the surface of the globe. Here
again I must beg my readers to take much of the evidence, which, if
expanded, would fill a volume, for granted, since it would be entirely
inappropriate here. But I may briefly state that animals are not
scattered over the surface of our globe at random, but that they are
associated together in what are called _faunae_, and that these
faunae have their homes within certain districts--called by naturalists
_zooelogical provinces_. The limits of these provinces are
absolutely fixed, in the ocean as well as on the land, by certain
physical conditions connected with climate, with altitude, 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 migrations are
periodical, and have boundaries as definite and impassable as those that
limit the permanent homes of animals. There is a certain series
established by the relations between different kinds of animals, as thus
distributed over the globe, which agrees with the gradation in their
rank, their growth, and their succession in time;--the law which
distributes animals in successive faunae, and in accordance both with
their relative superiority or inferiority, and with the physical
conditions essential to their existence, being the same as that which
controls their structural relations, their embryological development,
and their succession in time.

What, then, does this correspondence between the Series of Rank, the
Series of Growth, the Series of Time, and the Series of Geographical
Distribution in the life of animals teach us? Surely not that the
connection between animals is a material one; for the same kind of
relation exists between lower and higher animals of one type or one
class to-day, in their structural features, in their embryological
growth, and in their geographical distribution, as we trace in their
order of succession in time; and therefore, if this kind of evidence
proves that the later animals are the descendants of the earlier in any
genealogical sense, it should also prove that the animals living in one
part of the earth at present grow out of animals living in another part,
and that the higher animals of one class as it exists now are developed
out of the lower ones. The first of these propositions needs no
refutation; and with regard to the second, all our investigations go to
show that every bei