THE PHILOSOPHY OF BIRDS’ NESTS. 213 
the absence of any sufficiently powerful stimulus to 
change or improvement. No one imagines that if an 
infant Arab could be transferred to Patagonia or to 
the Highlands, it would, when it grew up, astonish 
its foster-parents by constructing a tent of skins. On 
the other hand, it is quite clear that physical condi- 
-tions, combined with the degree of civilization arrived 
at, almost necessitate certain types of structure. The 
turf, or stones, or snow—the palm-leaves, bamboo, or 
branches, which are the materials of houses in various 
countries, are used because nothing else is so readily 
to be obtained. The Egyptian peasant has none of 
these, not even wood. What, then, can he use but 
mud? In tropical forest-countries, the bamboo and the 
broad palm-leaves are the natural material for houses, 
and the form and mode of structure will be decided 
in part by the nature of the country, whether hot or 
cool, whether swampy or dry, whether rocky or plain, 
whether frequented by wild beasts, or whether subject 
to the attacks of enemies. When once a particular 
mode of building has been adopted, and has become 
confirmed by habit and by hereditary custom, it will 
be long retained, even when its utility has been lost 
through changed conditions, or through migration into 
avery different region. As a general rule, through- 
out the whole continent of America, native houses are 
built directly upon the ground—strength and security 
being given by thickening the low walls and the roof. 
In almost the whole of the Malay Islands, on the 
contrary, the houses are raised on posts, often to a 
