200 SEXUAL SELECTION: BIRDS. [Part II. 



scarlet ibis and to many herons, and from the analogy of 

 the species in the first class, that such colors have been 

 acquired through sexual selection by the nearly mature 

 males ; but that, differently from what occurs in the first 

 two classes, the transmission, though limited to the same 

 age, has not been limited to the same sex. Consequently 

 both sexes, when mature, resemble each other and differ 

 from the young. 



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 

 colored, resemble each other. Such cases are, I think, 

 more common t]?an those in the last class. We have in 

 England instances in the kingfisher, some woodpeckers, 

 the jay, magpie, crow, and many small dull-colored birds, 

 such as the hedge-warbler or kitty-wren. But the simi- 

 larity in plumage between the young and the old is never 

 absolutely complete, and graduates away into dissimilari- 

 ty. Thus the young of some members of the kingfisher 

 family are not only less vividly colored than the adults, 

 but many of the feathers on the lower surface are edged 

 with brown 2T — 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, while the young of other species differ 

 considerably from their parents of both sexes, which are 

 alike. 28 Both sexes and the young of the common jay are 

 closely similar; but in the Canada jay (Perisoreus Cana- 

 densis) the young differ so much from their parents that 

 they were formerly described as distinct species. 5 



29 



27 Jerdon, 'Birds of India,' vol. i. pp. 222, 228. Gould's 'Hand-book 

 of the Birds of Australia,' vol. i. pp. 124, 130. 



28 Gould, Ibid. vol. ii. pp. 37, 46, 56. 



29 Audubon, ' Ornith. Biography,' vol. ii. p. 55. 



