1/6 EVOLUTION OF TO-DAY. 



came inhabited by marsupials. Meantime, there 

 appeared in Europe some representatives of the true 

 mammals, which were of a higher order than mar- 

 supials, and quickly began to contend with and ex- 

 terminate them. These new mammals began to 

 spread from their point of origin over the eastern 

 and western continents ; destroying the marsupials 

 as they came into competition with them. They 

 thus caused the complete extinction of the latter 

 group over all the eastern continent except Aus- 

 tralia, which had in the meantime become separated 

 from Asia. On the western continent, too, the vic- 

 torious mammals destroyed all marsupials except 

 one single family, which, for some reason, succeeded 

 in maintaining its existence. This was the opossum, 

 which is found in North and South America ; and 

 thus we see the final result to be that, of the 

 formerly widely distributed order, representatives 

 are left in only two localities, separated from each 

 other by half the globe. All of this time the species 

 and genera have been constantly changing, so that 

 the families now living are very different from those 

 of the earlier ages. And so in other cases. The 

 tendency of the evidence seems to show that mam- 

 mals originated in Europe, or north of Europe, and 

 then migrated east, west, and south, finally thus 

 filling the whole world, except oceanic islands. 



Zoological Regions. 



Turning now from the past to the present, let us 

 first notice how far anatomical relationship is parallel 

 with geographical relationship. One prominent fact 



