Like most of the group to which it belongs, this honey-eater (_Tropidorhynchus bouruensis_) is a soberly coloured bird, but is noisy, active, and aggressive. _By permission of Messrs Hutchinson & Co._ Bouru Oriole 222 This “mimicking” oriole (_Oriolus bouruensis_) is of the same tone of colour as its supposed model the Friar-bird of the same island. _By permission of Messrs Hutchinson & Co._ King-Crow or Drongo 232 This very conspicuous black bird (_Dicrurus ater_), ranging from Africa to China, is a striking feature of the landscape wherever it occurs. _By permission of Messrs Hutchinson & Co._ Drongo-Cuckoo 232 The fork of the tail in this bird is unique among cuckoos, but is nevertheless much less developed than in the supposed model, and may be an adaptation for evolutions in flight, as such tails usually appear to be. _By permission of Messrs Hutchinson & Co._ Shikra Hawk 236 The upper surface of the tail, not shown in this drawing, exactly corresponds with that of the cuckoo “mimic.” _By permission of Messrs Hutchinson & Co._ Hawk-Cuckoo 236 This species (_Hierococcyx varius_) is commonly known in India as the “Brain-fever bird.” _By permission of Messrs Hutchinson & Co._ Brazilian Troupial 284 This species (_Icterus vulgaris_) is that most frequently seen in captivity; the pattern of colour is found in several other allied forms. _By permission of Messrs Hutchinson & Co._ Indian Black-Headed Oriole 284 Several other orioles besides this (_O. melanocephalus_) have the black head. _By permission of Messrs Hutchinson & Co._ Queen Whydah 298 This species (_Tetraenura regia_) is a typical example of seasonal sexual dimorphism, the male being long-tailed and conspicuously coloured only during the breeding season, and at other times resembling the sparrow-like female. _By permission of the Foreign Bird Club._ Courtship of Skylark 314 Illustrating display by a species with no decorative colouring or sex difference. THE MAKING OF SPECIES CHAPTER I RISE OF THE THEORY OF NATURAL SELECTION AND ITS SUBSEQUENT DEVELOPMENT