30 CHELTENHAM COLLEGE NATURAL HISTORY SOCIETY. 
weeks are helpless and dependent on the old birds generally hatch 
from comparatively smaller eggs. 
In all the theories which we have dealt with so far the bird’s own 
individuality may be almost neglected, Nature causing variations 
without any consciousness on the part of the bird. Now, I wish to 
speak of some theories regarding birds where the individuality is 
allowed some play. These theories will deal with song, nest-making, 
so-called instinctive fear, and migration. One of two theories used 
to be held with regard to these points. The one was that birds 
in these respects had always acted exactly as they do at present, and 
that they inherited a tendency to act only in these ways. A second 
theory was that though the peculiarities might have been acquired by 
some particular ancestor, yet that by their descendants these fixed 
habits were inherited as instincts and that the individual had very 
little power of varying. The theory held at the present day is that 
these so-called instincts are to a certain extent hereditary habits, but 
that they also depend upon traditions handed down from one generation 
to another, that, in fact, most of the acts are at any rate in some 
degree the result of imitation. 
Let us first take the case of song.—If eggs be taken early from the 
nest of the parent and placed in the nest of some other bird, 
the young when they are hatched very rarely attain to perfection in 
their own song, though, of course, there may be circumstances which 
prevent their imitating the song of their foster-parent, as a different 
form of vocal organs, which may make a very limited range of notes 
possible. As we might expect when it is absolutely necessary that 
the young bird should recognise a sound, as in the case of the 
warning cry, it seems to be hatched with the instinctive recognition of 
it perfect. In some cases it seems perfect whilst the young is still 
in the egg, for if it is tapping at the shell, and the hen utters 
the warning cry it will at once Stop. After two days, the young 
if taken away from the parents will, when their time to sing 
comes, produce some of the song-notes of the species. 
I think one may notice that in the case of those birds who have 
a very varied song the young are hatched helpless and are dependent 
on the parents for some time, and so have opportunities of learning 
a song, whereas when they are precocious their utterance is limited 
to a cry, as the cry of our domestic birds and of game. 
Nest building gives another example of an instinct which has to 
be supplemented by imitation. If an egg be taken and hatched 
artificially the bird will make the characteristic nest of the species 
