180 
SEXUAL SELECTION: BIKDS. 
Part II. 
furnislied with a tuft of bristles on the breast, but in 
two-year-old birds the tuft is about four inches long in 
the male and hardly apparent in the female ; when, 
however, the latter has reached her fourth year, it is 
from four to five inches in Jength.^^ 
In these cases, the females follow a normal course of 
development in ultimately becoming like the males ; and 
such cases must not be confounded with those in which 
diseased or old females assume masculine characters, 
or with those in which perfectly fertile females, whilst 
young, acquire through variation or some unknown cause 
the characters of the male.^^^ But all these cases have 
so much in common that they depend, according to the 
hypothesis of pangenesis, on gemmules derived from each 
part of the male being present, though latent, in the fe- 
male; their development following on some slight change 
in the elective afiSnities of her constituent tissues. 
A few words must be added on changes of plumage 
in relation to the season of the year. From reasons 
formerly assigned there can be little doubt that the 
elegant plumes, long pendant feathers, crests, &c., of 
egrets, herons, and many other birds, which are deve- 
loped and retained only during the summer, serve 
exclusively for ornamental or nuptial purposes, though 
29 On Ardetta, Translation of Cuvier's ‘ Kegne Animal/ by Mr. Blytb, 
footnote, p. 159. On the Peregrine Falcon, Mr. Blytli, in Charles- 
wortli’s ‘ Mag. of Nat. Hist.’ vol. i. 1837, p. 301. On Dicrurus, ‘Ibis,’ 
1863, p. 44. On the Platalea, ‘Ibis/ vol. vi. 1864, p. 366. On the 
Bombycilla, Audubon’s ‘ Ornitholog. Biography,’ vol. i. p. 229. On 
the Palseornis, see, also, Jerdon, ‘Birds of India,’ vol. i. j). 263. 
On the wild turkey, Audubon, ibid. vol. i. p. 15 : I hear from Judge 
Caton that in Illinois the female very rarely acquires a tuft. 
30 Mr. Blyth has recorded (Translation of Cuvier’s ‘ Kegne Animal,’ 
p. 158) various instances with Lanius, Kuticilla, Linaria, and Anas. 
Audubon has also recorded a similar case (‘ Ornith. Biog.’ vol. v. p. 519) 
^sdth Tyranga sestiva. 
