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 greater age than the strata with corresponding remains elsewhere; that in South America various species and genera of men existed in tertiary times, some of them at least as advanced as fairly well advanced modern savages; that there existed various land bridges between South America and other southern continents, including Africa; and that the ancestral types of modern mammals and of man himself wandered across one of these bridges to the old world, and that thence their remote descendants, after ages of time, returned to the new.  In addition to valuable investigations of fossil-bearing beds in the Argentine, he made some excellent general suggestions, such as that the pithecoid apes, like the baboons, do not stand in the line of man’s ancestral