Certain birds are parasitic, in this sense, that they compel or induce other birds to perform the labour of incubation and of rearing their young. The Rhea or Ostrich of South America is parasitical on its own species; the females laying each several eggs in the nests of several other females, and the male ostrich taking all the cares of incubation. More familiar examples, however, occur in our own Cuckoo, and in the Cowpen birds (_Molothrus_ _pecoris_ and _M. niger_) of North and South America. "These fasten themselves," as has been remarked by Mr Swainson, "on another living animal, whose animal heat brings their young into life, whose food they live upon, and whose death would cause theirs during the period of infancy." The habit, at least in the case of the European Cuckoo, is so well known, that I need not do more than merely allude to the fact, that the female seeks for the nests of other insect-eating birds, always much smaller than itself, and deposits its own eggs,--a single egg in each; that this stranger egg is hatched by the foster-mother with all care, and the young bird is nurtured with all tenderness even at the expense of its own proper eggs and young, which in general are sacrificed in the course of the process. Every schoolboy knows these facts, but few perhaps have ever suspected the existence of a romantic feeling of love and fealty in the little bird towards the cuckoo herself, prompting the rendering of the service required as a coveted honour. Yet a naturalist has communicated to Mr Yarrell some facts which certainly look this way; and because they are indubitably the very romance of natural history, I cite them, leaving my readers to judge of their value. "As you have contributed," writes Mr W. C. Newby of Stockton, "so much to the information and amusement of the numerous class of readers who take an interest in subjects of natural history, I consider it my duty to communicate first to you, what appears to me a new fact in the habits and character of that general favourite the cuckoo.