146 INSECUTOR INSCITI/E MENSTRUUS 



The whole Peruvian montanya, combined with that of Bolivia on the 

 south and Ecuador and Colombia on the north, constitutes the most pro- 

 lific biotic region on earth. This results from its natural advantages in 

 this respect. Situated at the base and especially on the lower half or 

 more of the slopes of the moist eastern exposure of the Andes, its axis 

 disposed nearly north and south, with the most extensive low-lying humid 

 tropical region on earth to draw from — the great Amazons-Orinoco-La 

 Plata tropical rain-forest region — it fumishes in its varying altitudes, lati- 

 tudes, slope exposures, and soil constitutions, with their dependent fluctua- 

 tions of meteorological, food-supply, and other environmental conditions, 

 the greatest variety of factors possible of attainment for the evolution of 

 forms of life. If the living forms exposed to such influences belong to 

 young and plastic stocks now in the evolutional prime of their unfolding 

 and specialization, at the climax of their susceptibility to variation and 

 adaptation, it is small wonder that they respond thereto in an excessive 

 profuseness of typical and transitional forms approximating the actueJ con- 

 ditions that the older types of life have passed through in their early 

 development. Here are verily exhibited to the biologist, if he have eyes 

 to see, the intricate processes involved in the origin of species. Here may 

 be witnessed genera in the making. Such conditions, it is true, exist to 

 an extent in other peirts of the world, but nowhere else on such a vast 

 and therefore highly illustrative scale as in the eastern foothill and moist- 

 slope region of the Andes. 



Considered as an active biotic entity, this montanya region extends in 

 latitude continuously north and northwest from Patagonia to Alaska, and 

 in altitude from the whole eastern base to the crests of the Andes and 

 their succeeding chains to the north, culminating in the Rocky Mountain 

 system, descending in places to the western base also. Its fauna through- 

 out and especially its basic or low-altitude to mean-altitude stocks are thus 

 assured access to every possible complex of climatic, topographic, and 

 geologic variations that will sustain life, in both horizontal and vertical 

 distribution zones, between opposed boreal parallels of latitude and 

 between sea-level and perpetual-snow altitudes. All of these complexes 

 have their respective distinct effects on food supply, interracial competi- 

 tion, life struggle, and general environment. From central to northern 

 Peru it laps over in its normal humid aspect into the canyon beds of the 

 western slopes of the Andes, at first between the 5,000-foot and 9,000- 

 foot levels but dropping in the north as low as 3,000 feet, and from the 



