CUCKOO. 
305 
creature. The cuckoo’s legs, however, seemed very muscular, 
and it appeared to feel about with its wings, which were abso- 
lutely featherless, as with hands — the 4 spurious wing’ (unusually 
large in proportion) looking like a spread-out thumb. The most 
singular thing of all was the direct purpose with which the blind 
little monster made for the open side of the nest, the only part 
where it could throw its burden down the bank. [The latter 
remark has reference to the position of the nest below a heather 
bush, on the declivity of a low abrupt bank, where the only 
chance of dislodging the young birds was to eject them over the 
side of the nest remote from its support upon the bank.] As 
the young cuckoo was blind, it must have known the part of 
the nest to choose by feeling from the inside that that part was 
unsupported. 
Such being the facts, we have next to ask how they 
are to be explained on the principles of evolution. At 
first sight it seems that although the habit saves the bird 
which practises it much time and trouble, and so is clearly 
of benefit to the individual, it is not so clear how the in- 
stinct is of benefit to the species; for as cuckoos are not 
social birds, and therefore cannot in any way depend on 
mutual co-operation, it is difficult to see that this saving 
of time and trouble to the individual can be of any use to 
the species. But Jenner seems to have hit the right 
cause in the concluding part of the above quotation. If 
it is an advantage that the cuckoo should migrate early, 
it clearly becomes an advantage, in order to admit of this, 
that the habit should be formed of leaving her eggs for 
other birds to incubate. At any rate, we have here a suffi- 
ciently probable explanation of the raison d'etre of this 
curious instinct ; and whether it is the true reason or the 
only reason, we are justified in setting down the instinct 
to the creating influence of natural selection. 
Mr. Darwin, in his 6 Origin of Species,’ has some in- 
teresting remarks to make on this subject. First, he 
is informed by Dr. Merrell that the American cuckoo, 
although as a rule following the ordinary custom of birds 
in incubating her own eggs, nevertheless occasionally de- 
posits them in the nests of other birds. 
Now let us suppose that the ancient progenitor of our Euro« 
pean cuckoo had the habits of the American cuckoo, and that 
