ORNITHOLOGY OF QUITO. 
only 37, dependent upon the climate, and its influence on insect 
and vegetable life. Of these 37 species, notwithstanding the great 
distance, 8 are still met with, which are at the same time common 
to the 15° of latitude, and to the mountain ranges, exceeding 
11,000 feet in elevation — leaving to this zone of latitude only 29 
as properly belonging to it. 
Observing the distribution according to elevation, D’Orbigny 
found, in the first zone, the pntire number of species only 83, of 
which 51 descend to the plains, leaving only 32 peculiar or proper 
to the mountains of this zone, or the warm region, which is ex- 
tremely few when compared with the number (189) proper to the 
^Equatorial plains. 
In the second zone of elevation, 60 species were observed, a 
number comparatively with the first zone of elevation as of three- 
fourths, and with the second zone of latitude which corresponds 
with it of one-twelfth. These comparisons show, that if there is a 
small relative proportion between the gradual diminution of the 
numbers incidental to the two first zones of latitude and elevation, 
there is a very large one between the numbers in the zone of lati- 
tude which corresponds with it. In this zone there are 31 species 
proper to the mountains. 
The third zone of elevation presents only 22 species, being, in 
comparison with the third zone of latitude which corresponds with 
it, of only four-sixteenths. Of the 22 species, 8 are also found 
between the 34° and 45° of south latitude ; whence it results, that 
there are only 14 species peculiar to these very elevated mountain 
ranges. 
These observations relate to the eastern aspect or exposure of 
the Andes, for on the opposite or western aspect, the discrepancy 
in numbers is very great. This is caused by the mountains on the 
one side being clothed with impenetrable forests, where fruitful 
rains encourage an active and luxuriant vegetation, and where 
their plains are covered with wood, interspersed with the variation 
of clumps and open glades, water, and marshy grounds. The west- 
ern slopes, on the contrary, scarcely exhibit a stunted brushwood, 
or groups of Cactus springing up from among the dry and parched 
rocks, where it seldom rains, and where the torrents are supplied 
by the perpetual snows of the elevated peaks. On the eastern 
slope, then, of the Andes, 374 species exist, while on the western 
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