Chap. XVI] THE YOUNG LIKE THE ADUL1 FEMALES. 181 



being spotted with bronze) the adult female in all respects, 

 including: the length of her tail, so that the tail of the male 

 actually becomes shorter as he reaches maturity, which is 

 a most unusual circumstance. 3 Again, the plumage of 

 the male goosander {JSIergus merganser) is more conspicu- 

 ously colored, with the scapular and secondary wing- 

 feathers much longer than in the female, but 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 resemble 

 in all respects the adult female, so that their crests are 

 actually of greater length, though narrower, than in the 

 adult male. 4 



When the young and the females closely resemble 

 each other and both differ from the male, the most obvious 

 conclusion is that the male alone has 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 unex- 

 plained cause, and transmitted in their diminished state to 

 their male offspring alone, when arrived at the correspond- 

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

 the male alone 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, 6 with respect to closely-allied 



3 I owe this information to Mr. Gould, who showed me the specimens : 

 see also his 'Introduction to the Trochilidae,' 1861, p. 120. 



4 Macgillivray, 'Hist. Brit. Birds^ol. v. pp. 207-214. 



5 See his admirable paper in the ' Journal of the Asiatic Soc. of Ben- 

 gal, 1 vol. xix. 1850, p: 223 ; see also Jerdon, 'Birds of India,' vol. i. in- 



