2283 THE PHILOSOPHY OF BIRDS NESTS. 
buildings, and some rocks where these birds build, he 
found many nests of the old type along with some of 
the new pattern. He then examined all the figures 
and descriptions of the older naturalists, and found 
that they invariably represented the older form only. 
The difference between the two forms he states to 
be as follows. In the old form the nest is a portion of 
a globe—when situated in the upper angle of a window 
one-fourth of a hemisphere—and the opening is very 
small and circular, being of asize just sufficient to allow 
the body of the bird to pass. In the new form the 
nest is much wider in proportion to its height, being 
a segment of a depressed spheroid, and the aperture 
is very wide and shallow, and close to the horizontal 
surface to which the nest is attached above. 
M. Pouchet thinks that the new form is an un- 
doubted improvement on the old. The nest has a 
wider bottom and must allow the young ones to have 
more freedom of motion than in the old narrower, and 
deeper nests, and its wide aperture allows the young 
birds to peep out and breathe the fresh air. This is 
so wide as to serve as a sort of balcony for them, and 
two young ones can often be seen on it without inter- 
fering with the passage in and out of the old birds. 
At the same time, by being so close to the roof, it is 
a better protection against rain, against cold, and 
against enemies, than the small round hole of the old 
nests. Here, then, we have an improvement in nest 
building, as well marked as any improvement that 
takes place in human dwellings in so short a time. 
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