Chap. XVI. THE YOUNG LIKE THE ADULT FEMALES. 189 



resemble (with the exception of the breast 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.^ Again, the plumage 

 of the male goosander {Mergus merganser) is more con- 

 spicuously coloured, with the scapular and secondary 

 winiT-feathers much lono^er than in the female, but differ- 

 ently from what occurs, as far as 1 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.^ 



When the young and the females closely resemble 

 each other and both differ from the male, the most ob- 

 vious conclusion is that the male alone has been modi- 

 fied. 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 elon- 

 gated 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 trans- 

 mitted in their diminished state to their male offspring 

 alone, when arrived at the corresponding age of ma- 

 turity. The belief tiiat in the present class the male 

 alone has been modified, as far as the differences be- 

 tween the male and the female together with her 

 young are concerned, is strongly supported by some 



' I owe this information to Mr. Gould who sliewed me the specimens; 

 see aLo his ' Introduction to the Trochilidte,' I8G1, p. 120. 

 * Maegillivray, ' Hist. Brit. Birds/ vol. v. p. 207-214. 



