VIPERA+PSEUDECHIS MAJOR. 185 
poisonous reptiles in temperate zones or cold climates and 
the same species in torrid zones. In the tropics, on the Andes 
Mountains, for example, this fact is so plainly evident that, 
by referring to the tabular list of snakes in Colombia, where 
the same species occur first in some States, they occupy a sec- 
ond, third, fourth, or fifth rank in other places or districts. 
The cause of this is that in different localities the same snake 
occurs in different isothermal zones. A Taya (Vipera pscud- 
echis major), for instance, found at a height of 200 metres 
above the sea-level, is much more venomous and invariably 
holds a greater quantity of poison in deposit, than one found 
on the Plains of Bogota, or at an elevation of 2300 metres. 
The one would have its corresponding parts so arranged 
and disposed as to hold a comparatively large quantity of 
venom in a poison-bladder; while the other, requiring and 
using a much smaller quantity, would have the duct from the 
poison-gland to the fang slightly enlarged near its attachment 
to the base of the latter, and consequently the poison-vesicle 
would be wanting. 
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