602 THE DESCENT OF MaN 



V. When the adults of both sexes have a distinct winter 

 and summer plumage, whether or not the male differs from 

 the female, the young resemble the adults of both sexes 

 in their winter dress, or much more rarely in their summer 

 dress, or they resemble the females alone. Or the young 

 may have an intermediate character; or, again, they may 

 differ greatly from the adults in both their seasonal 

 plumages. 



VI. In some few cases the young in their first plumage 

 differ from each other according to sex, the young males re- 

 sembling more or less closely the adult males, and the young 

 females more or less closely the adult females. 



Class I. — In this class, the young of both sexes more or 

 less closely resemble the adult female, while the adult male 

 differs from the adult female, often in the most conspicuous 

 manner. Innumerable instances in all Orders could be given; 

 it will suffice to call to mind the common pheasant, duck, and 

 house-sparrow. The cases under this class graduate into 

 others. Thus the two sexes when adult may differ so 

 slightly, and the young so slightly from the adults, that 

 it is doubtful whether such cases ought to come under the 

 present, or under the third or fourth classes. So, again, 

 the young o£ the two sexes, instead of being quite alike, 

 may differ in a slight degree from each other, as in our 

 sixth class. These transitional cases, however, are few, or 

 at least are not strongly pronounced, in comparison with 

 those which come strictly under the present class. 



The force of the present law is well shown in those 

 groups in which, as a general rule, the two sexes and the 

 young are all alike; for when in these groups the male 

 does differ from the female, as with certain parrots, king- 

 fishers, pigeons, etc., the young of both sexes resemble the 

 adult female." "We see the same fact exhibited still more 



' See, for instance, Mr. Gould's account ("Handbook to the Birds of Aus- 

 tralia," vol. i. p. 133) of Cyanalcyon (one of the Kingfishers), in which, how- 

 ever, the young male, though resembling the adult female, is less brilliantly 



