WHY DO THE BIRDS BUILD SO? 105 
our limits. The subject is in itself a study, and a 
literature already. 
Before we close, however, let us glance a mo- 
ment at the probable origin and development of nest 
building. 
While we have fossil birds, and fossil eggs even, 
it is unfortunate for us that we have no fossil nests. 
Neither have we an embryology of nests in the true 
sense from which we may infer something of their 
beginnings. Young birds build cruder nests than 
their parents do, but this is a matter purely doubtless 
of experience or the lack of it. Still it is a law that 
if the individual can progress then so may the race. 
We have seen that birds may grow more expert under 
changed conditions. We have also some hints of the 
route up which modern nest building has come through 
the study of the nests of the lowest birds now living. 
While some fishes now build nests, there is noth- 
ing of the kind among the reptiles, except perhaps one 
of the snakes of India, and the hotbed habits of some 
crocodiles already noted. The nest, therefore, as we 
know it has been developed wholly within the birds, 
and, like incubation, is not an inheritance. 
As a simple cup-shaped depression in the bare 
sand or earth, it may have indeed been the same as 
the reptiles’ sand scrape with the lid left off for incu- 
bating. Many birds yet use such a pretense, and a 
few, especially among those laying only one or two 
egos, hatch their young out on bare flat surfaces, as 
rocks, ete. 
Doubtless, however, the first step toward a nest 
