124 CUCKOW 
becoming hereditary, it will be seen that it requires but an applica- 
tion of the principle of ‘“ Natural Selection” to shew the probability 
of this principle operating in the course of time to produce the facts 
asserted by Atlian, by the anonymous Solognot of the last century, 
and by Dr. Baldamus and others since. The particular gens of 
Cuckow which inherited and transmitted the habit of depositing in 
the nest of any particular species of bird eggs having more or less 
resemblance to the eggs of that species would prosper most in those 
members of the gens where the likeness was strongest, and the other 
members would (cxteris paribus) in time be eliminated. As already 
shewn, it is not to be supposed that all species, or even all 
individuals of a species, are duped with equal ease. The operation 
of this kind of natural selection would be most needed in those 
cases where the species are not easily duped,—that is, in those 
cases which occur the least frequently. Here it is we find it, for 
observation shews that eggs of the Cuckow deposited in nests of 
the Red-Backed Shrike (Lanius collwrio), of the Bunting (Emberiza 
miliaria), of the Redstart (Ruticilla phenicura), and of the Icterine 
Warbler approximate in their colouring to eggs of those species— 
species in whose nests the Cuckow rarely (in comparison with 
others) deposits eggs. Of species which are more easily duped, 
such as the Hedge-Sparrow, mention has already been made. 
More or less nearly allied to our Cuckow are many other forms 
of the genus from various parts of Africa, Asia, and their islands, 
while one even reaches Australia. How many of these deserve 
specific recognition will long be a question among ornithologists 
which need not be discussed here. In some cases the chief differ- 
ence is said to lie in the diversity of voice—a character only to be 
appreciated by those acquainted with the living birds, and though 
of course some regard should be paid to this distinction, the possi- 
bility of birds using different “dialects” according to the locality 
they inhabit (see SONG) must make it a slender specific diagnostic. 
All these forms are believed to have essentially the same habits as 
our Cuckow, and, as regards parasitism, the same is to be said of 
the large Cuckow of Southern Europe and North Africa, Coccystes 
glandarius, which victimizes Pies (Pica mauritanica and Cyanopica 
cooki) and Crows (Corvus cornix). ‘True it is that an instance of this 
species, commonly known as the Great Spotted Cuckow, having 
built a nest and hatched its young is on record, but this is a mani- 
fest error (cf. Salvadori, Uccelli d'Italia, pl. 42); the later observa- 
tions of Dr. A. E. Brehm, Canon Tristram, Stafford Allen, and 
others leave no doubt on the subject. It is worthy of remark that 
the eggs of this bird so closely resemble those of one of the Pies in 
whose nest they have been found, that even expert oologists have 
been deceived by them, only to discover the truth when the 
Cuckow’s embryo had been extracted from the supposed Pie’s egg. 
