Thus he separates the birds of prey into three great groups - (I) the ordinary Diurnal forms, including the Falconidae and Vulturidae of the systematist of his time; but distinguishing the American Vultures from those of the Old World; (2) Gypogeranus, the secretary-bird; and (3) the owls (q.v.).
Poulton, in an admirable discussion of contemporary views regarding species (presidential address to the Entomological Society of London 1904), has shown that Darwin did not believe in the objective existence of species, not only because he was led to discard the hypothesis of special creation as the explanation of the polymorphism of life, but because in practice as a working systematist he could neither find for himself nor ascertain from other systematists any settled criteria by which a group of specimens could be elevated into a genus, accepted as a species, or regarded as a variety.
Thus not only did Darwin's theory give a new basis to the study of organic 'structure, but, whilst rendering the general theory of organic evolution equally acceptable and Effects of necessary, it explained the existence of low and simple forms of life as survivals of the earliest ancestry of theory more highly complex forms, and revealed the classifications of the systematist as unconscious attempts to construct the genealogical tree or pedigree of plants and animals.
Premising then that the chief characters assigned by this systematist to his several groups are drawn from almost all parts of the structure of birds, and are supplemented by some others of their more prominent peculiarities, we present the following abstract of his scheme:-2 I.