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 then 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 then 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 feeding old birds of a distinct kind and clamouring 

 to be fed by them. The parasitic habits of another species of 

 Melothrus f the M. Canariensis, 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 extia- 

 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 



