humming-birds) differs conspicuously from the female in having a
splendid gorget and fine ear-tufts, but the female is remarkable from
having a much longer tail than that of the male; now the young of both
sexes resemble (with the exception of the breast being spotted with
bronze) the adult female in all other 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. I owe this
information to Mr. Gould, who shewed me the specimens; see also his
Introduction to the Trochilidae, 1861, p. 120.) Again, the plumage of
the male goosander (Mergus merganser) is more conspicuously coloured
than that of the female, with the scapular and secondary wing-feathers
much longer; 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 entirely resemble the adult female, so that
their crests are actually of greater length, though narrower, than in
the adult male. (4. Macgillivray, Hist. Brit. Birds, vol. v. pp.
207-214.)
When the young and the females closely resemble each other and both
differ from the males, the most obvious conclusion 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 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 (5. See his admirable paper in the Journal of the Asiatic
Soc. of Bengal, vol. xix. 1850, p. 223; see also Jerdon, Birds of
India, vol. i. introduction, p. xxix. In regard to Tanysiptera, Prof.
Schlegel told Mr. Blyth that he could distinguish several distinct
races, solely by comparing the adult males.), 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
491