188 
SEXUAL SELECTION: BIRDS. 
PiHT J 
manner, from the adult female. Innumerable instaD c ^ 
in all Orders could be given ; it will suffice to caU f 
mind the common pheasant, duck' and house-spa 1 ' 1 * ' 0 *! 
The eases under this class graduate into others. 
the two sexes when adult may differ so slightlv, and 1 ■ . 
young so slightly from the adults, that it is doubtf ' 1 
whether such cases ought to come under the present ' 0 
under the third or fourth classes. So again the y° l! '!;' 
of both sexes, instead of being quite alike, may 
in a slight degree from each other, as in our sixth d a " 
These transitional cases, however, are few in nun 1 ^'’ 
or at least are not strongly pronounced, in compad^ 
with those which come strictly under the present d® 8 * 
The force of the present law is well shewn in , 
groups, in which, as a general rule, the two sexes ^ 
the young are all alike; for when the male in ^- ie \ 
groups does differ from the female, as with certain 
rots, kingfishers, pigeons, &c., the young of both 
resemble the adult female * * * . 2 We see the same fad e , 
hibited still more clearly in certain anomalous c® 9 ^, 
thus the male of HeliotJvrix auriculata (one of the h"’!^ 
ming-birds) differs conspicuously from the feinal 0 * 
having a splendid gorget and fine ear-tufts, but * j 
female is remarkable from having a much long e1 ' ^ 
than that of the male ; now the young of both 
2 for instance, Mr. Gould’s account (*. Handbook of tlie Jj. 
Australia, vol. i. p. 133) of Cyanalcyon (one of the Kingfishers) iu '1 1 j, 
however, the young male, though resembling the adult femah', 10 i,juC 
brilliantly coloured. In some species of Duccio the males l«‘ r ° > 
tails, and the females browu ones ; ami Mr. it. B. Sharpe i u,br f Lii' 
that the tail of the young male of D. Gaudichaudi is at firs 1 11 ,, ; ;i 
Mr. Gould has described (ibid. vol. ii. p. 14, 20, 37) the se* e %.ifl> 
the young of certain Black Cockatoos aud of the King Lory . ji. 
which the same rule prevails. Also Jordon (‘Birds of India,’ vt “' Jje 
260) on the Falseornu roea, in which the young are more 
female than the male. See Audubon (* Ornith. Biograph.’ vol' 
475) on the two sexes and the young of Columba passerine 
