BIRDS. 533 



differently from what occurs, as far as I know in any other 

 bird, the crest of the adult male, though broader than that 

 of the female, is considerably shorter, being only a little 

 above an inch in length; the crest of the female being two 

 and a half inches long. Now the young of both sexes 

 entirely resemble the adult female, so that their crests are 

 actually of greater length, though narrower than in the 

 adult male.* 



When the young and the females closely resemble each 

 other and both differ from the males, the most obvious con- 

 clusion is that the males alone have been modified. Even 

 in the anomalous cases of the Heliothrix and Mergus, it is 

 probable that originally both adult sexes were furnished 

 the one species with a much elongated tail and the other 

 with a much elongated crest these characters having since 

 been partially lost by the adult males from some unexplained 

 cause, and transmitted in their diminished state to their 

 male offspring alone, when arrived at the corresponding 

 age of maturity. The belief that in the present class the 

 male aloin has been modified, as far as the differences 

 between the male and the female together with her young 

 are concerned, is strongly supported by some remarkable 

 facts recorded by Mr. Blyth,t with respect to closely allied 

 species which represent each other in distinct countries. 

 For with several of these representative species the adult 

 males have undergone a certain amount of change and can 

 be distinguished; the females and the young from the dis- 

 tinct countries being indistinguishable, and therefore 

 absolutely unchanged. This is the case with certain 

 Indian chats (Thamnobia), with certain honey-suckers (Nec- 

 tarinia), shrikes (Tephrodornis), certain kingfishers (Tany- 

 siptera), Kalij pheasants (Gallophasis) and tree-partridges 

 (Arboricola). 



In some analogous cases, namely, with birds having a 

 different summer and winter plumage, but with the two sexes 

 nearly alike, certain closely allied species can easily be dis- 

 tinguished in their summer or nuptial plumage, yet are 



* Macgillivray, ' Hist. Brit. Birds," vol. v, pp. 207, 214. 



t See his admirable paper in the "Journal of tlie Asiatic Soc. of 

 Bengal," vol xix. 1850, p. 223; see also Jerdon, " Birds of India," 

 vol. i, introduction, p. 29. In regard to Tanysiptera, Prof. Sclilegel 

 told Mr. Blytb that he could distinguish several distinct races, solely 

 by comparing the adult males. 



