Felidae, the stag, and the antelope. Man himself has, no doubt, been
under the same law, and is probably a much larger animal than any of
his Tertiary ancestors. In the vegetable world this process, in many
cases, at least, has been reversed, and the huge treelike
club-mosses and horsetails of Carboniferous times have dwindled in
our time to very insignificant herbaceous forms.

Animals of overweening size are handicapped in many ways, so that
nature in most cases finally abandons the gigantic and sticks to the
medium and the small.




III



Can we fail to see the significance of the order in which life has
appeared upon the globe--the ascending series from the simple to the
more and more complex? Can we doubt that each series is the outcome
of the one below it--that there is a logical sequence from the
protozoa up through the invertebrates, the vertebrates, to man? Is
it not like all that we know of the method of nature? Could we
substitute the life of one period for that of another without doing
obvious violence to the logic of nature? Is there no fundamental
reason for the gradation we behold?

All animal life lowest in organization is earliest in time, and vice
versa, the different classes of a sub-kingdom, and the different