490 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
fested in various stages of development by certain existing repre- 
sentatives of the Cuculide. 
Concerning the origin of these instincts and habits, the theory 
that natural selection, acting during a long period of time upon a 
chance beneficial variation in habits displayed by an early progenitor 
of the race, is responsible for the habit, receives much support from 
a further fact. Certain birds have been known to lay eggs in the 
nests of others belonging to widely different genera, moor hens’ eggs 
have been found in a coot’s nest, and an egg of the former species 
was taken in the half-finished home of a blackbird. Starlings eject 
woodpeckers from their nesting-holes in trees, and eggs of gulls 
and eider ducks have been noticed in each other’s nests. Romanes 
in his “Animal Intelligence” says that we are justified in setting 
down the cuckoo instinct to the creating influence of natural selec- 
tion, and a consideration of the facts just mentioned will show how 
easily the parasitic instinct may have originated. The practice is 
by no means confined to birds, and an interesting comparison may 
be made between birds and insects by referring to the habits of a 
certain kind of bee, which always consigns its eggs to the care of 
another species. These parasitical insects are structurally modified 
in obedience to the law of coordination of structure with function 
and habit, for they are devoid of the pollen-gathering apparatus, 
which would have been absolutely essential had they been obliged to 
rear their own offspring. 
There are two other phases of the cuckoo problem that I should 
like to touch upon briefly, viz: 
(1) The resemblance that certain cuckoos’ eggs bear to those of 
the chosen foster parent. 
(2) The nature of the impulse acting on a newly-born cuckoo and 
causing it to eject its fellow-nestlings from their home. 
As regards the first much debated point, it is interesting to note 
that the great spotted cuckoo (C. glandarius) of South Africa lays 
eggs closely resembling those of certain crows and magpies which 
constitute its victims. Other members of the Cuculide, especially 
some of the Australian species, do the same thing. The salmon- 
tinted egg of the pallid cuckoo (C. pallidus) is frequently found 
among a clutch of flesh-colored honey eaters’ eggs; the narrow-billed 
bronze cuckoo (C. basalis) favors the blue wren (J/. cyaneus), with 
her tiny pink-spotted egg; and most wonderful of all is the fan- 
tailed cuckoo (C. flabelliformis). I have found a great number of 
the eggs of the last-named species in nests of the white-browed scrub 
wren (Sericornis frontalis), and in several instances the resemblance 
between the eggs of foster parents and cuckoo has been most pro- 
nounced. 
