unted for by the existence of some former
direct land bridge extending, for instance, between Patagonia and
Australia, or between Brazil and South Africa, or between the West
Indies and the Mediterranean, or between a part of the Andean region
and northeastern Asia. The trouble is that as more groups of animals
are studied from the standpoint of this hypothesis the number of such
land bridges demanded to account for the existing facts of animal
distribution is constantly and indefinitely extended. A recent book by
one of the most learned advocates of this hypothesis calls for at
least ten such land bridges between South America and all the other
continents, present and past, of the world since a period geologically
not very remote. These land bridges, moreover, must, many of them,
have been literally bridges; long, narrow tongues of land thrust in
every direction across the broad oceans. According to this view the
continental land masses have been in a fairly fluid condition of
instability. By parity of reasoning, the land bridges could be made a
hundred instead of merely ten in number. The facts of distribution are
in many cases inexplicable with our present knowledge; yet if the
existence of widely separated but closely allied forms is habitually
to be explained in accordance with the views of the extremists of this
school we could, from the exclusive study of certain groups of
animals, conclude that at different periods the United States and
almost every other portion of the earth were connected by land and
severed from all other regions by water--and, from the study of
certain other groups of animals, arrive at directly opposite and
incompatible conclusions.

The most brilliant and unsafe exponent of this school was Ameghino,
who possessed and abused two gifts, both essential to the highest type
of scientist, and both mischievous unless this scientist possess a
rare and accurate habit of thought joined to industry and mastery of
detail:--namely, the gift of clear and interesting writing, and the
gift of generalization. Ameghino rendered marked services to
paleontology. But he generalized with complete recklessness from the
slenderest data; and even these data he often completely misunderstood
or misinterpreted. His favorite thesis included the origin of
mammalian life and of man himself in southernmost South America, with,
as incidents, the belief that the mammalian-bearing strata of South
America were of much grea