CUCKOO. 
309 
must be dismissed as too seriously encumbered by the 
difficulties which I have mentioned. We may with philo- 
sophical safety invoke the influence of natural selection to 
explain all cases of protective colouring when the modus 
operandi need only be supposed simple and direct ; but 
in a case such as this the number and complexity of the 
conditions that would require to meet in order to give 
natural selection the possibility of entrance., seem to me 
much too considerable to admit of our entertaining the 
possibility of its action — at all events in the way that 
Professor Newton suggests. Therefore, if the facts are 
facts, I cannot see how they are to be explained. 
Cuckoos are not the only birds which manifest the 
parasitic habit of laying their eggs in other birds’ nests. 
Some species of Melothrus , a widely distinct genus of 
American birds, allied to our starlings, have parasitic habits 
like those of the cuckoo ; and the species present an interesting 
gradation in the perfection of their instincts. The sexes of 
Melothrus cadius are stated by an excellent observer, Mr. 
Hudson, sometimes to live promiscuously together in flocks and 
sometimes to pair. They either build a nest of their own, or 
seize on one belonging to some other bird, occasionally throwing 
out the nestlings of the stranger. They either lay their eggs in 
the nest thus appropriated, or oddly enough build one for them- 
selves on the top of it. They usually sit on their own eggs and 
rear their own young ; but Mr. Hudson says it is probable that 
they are occasionally parasitic, for he has seen the young of this 
species following old birds of a distinct kind and clamouring 
to be fed by them. The parasitic habits of another species of 
Melothrus , the M. Ganariensis , are much more highly developed 
than those of the last, but are still far from perfect. This bird, 
as far as it is known, invariably lays its eggs in the nests of 
strangers, but it is remarkable that several together sometimes 
commence to build an irregular untidy nest of their own, placed 
in singularly ill-adapted situations, as on the leaves of a large 
thistle. They must, however, as far as Mr. Hudson has ascer- 
tained, complete a nest for themselves. They often lay so many 
eggs, from fifteen to twenty, in the same foster- nest, that few or 
none can possibly be hatched. They have, moreover, the extra- 
ordinary habit of pecking holes in the eggs, whether of their 
own species or of their foster-parents, which they find in the 
appropriated nests. They drop also many eggs on the bare 
