The Theory of Sexual Selection. 381 
may find lying about the woods and fields. In many 
cases a marked preference is shown for particular 
objects—as, for instance, in the case of the Syrian 
nut-hatch, which chooses the iridescent wings of 
insects, or that of the great crested fly-catcher, which 
similarly chooses the cast-off skins of snakes. But 
no doubt the most remarkable of these cases is that 
of the baya-bird of Asia, which after having com- 
pleted its bottle-shaped and chambered nest}, studs it 
over with small lumps of clay, both inside and out, 
upon which the cock-bird sticks fire-flies, apparently 
for the sole purpose of securing a brilliantly decorative 
effect. Other birds, such as the hammer-head of 
Africa, adorn the surroundings of their nests (which 
are built upon the ground) with shells, bones, pieces 
of broken glass and earthenware, or any objects of a 
bright and conspicuous character which they may 
happen to find. The most consummate artists in this 
respect are, however, the bower-birds; for the species 
of this family construct elaborate play-houses in the 
form of arched tunnels, built of twigs upon the ground. 
Through and around such a tunnel they chase one 
another ; and it is always observable that not only is 
the floor paved with a great collection of shells, bones, 
coloured stones, and any other brilliant objects which 
they are able to carry in their beaks, but also that the 
walls are decorated with the most gaudy articles 
which the birds can find. There is one genus, in 
Papua, which even goes so far as to provide the 
theatre with a surrounding garden. A level piece of 
1 The chambers are three in number. The two upper ones are 
occupied respectively by the male and the sitting female. The lower 
one serves as a general living room when the young are hatched. 
