CLASS IV. _When the adult male resembles the adult female, the young of both sexes in their first plumage resemble the adults._—In this class the young and the adults of both sexes, whether brilliantly or obscurely coloured, resemble each other. Such cases are, I think, more common than those in the last class. We have in England instances in the kingfisher, some woodpeckers, the jay, magpie, crow, and many small dull-coloured birds, such as the hedge-warbler or kitty-wren. But the similarity in plumage between the young and the old is never absolutely complete, and graduates away into dissimilarity. Thus the young of some members of the kingfisher family are not only less vividly coloured than the adults, but many of the feathers on the lower surface are edged with brown,[255]—a vestige probably of a former state of the plumage. Frequently in the same group of birds, even within the same genus, for instance in an Australian genus of parrokeets (Platycercus), the young of some species closely resemble, whilst the young of other species differ considerably from their parents of both sexes, which are alike.[256] Both sexes and the young of the common jay are closely similar; but in the Canada jay (_Perisoreus canadensis_) the young differ so much from their parents that they were formerly described as distinct species.[257] Before proceeding, I may remark that under the present and two next classes of cases the facts are so complex, and the conclusions so doubtful, that any one who feels no especial interest in the subject had better pass them over.