218 
SEXUAL SELECTION: BIRDS. 
Paet II. 
waders. Lastly, in regard to the young differing 
greatly from both sexes in their adult summer and 
winter plumages, this occurs with some herons and 
egrets of North America and India, — the young alone 
being white. 
I will make only a few remarks on these complicated 
cases. When the young resemble the female in her 
summer dress, or the adults of both sexes in their winter 
dress, the cases differ from those given under Classes I. 
and III. only in the characters originally acquired by 
the males during the breeding-season, having been 
Imited in their transmission to the corresponding season. 
When the adults have a distinct summer and winter 
plumage, and the young differ from both, the case is 
more difficult to understand. We may admit as pro- 
bable that the young have retained an ancient state 
of plumage ; we can account through sexual selection 
for the summer or nuptial plumage of the adults, but 
how are we to account for their distinct winter plumage ? 
If we could admit that this plumage serves in all cases 
as a protection, its acquirement would be a simple 
affair ; but there seems no good reason for this ad- 
mission. It may be suggested that the widely different 
conditions of life during the winter and summer have 
acted in a direct manner on the plumage; this may 
have had some effect, but I have not much confidence 
in so great a difference, as we sometimes see, between 
the two plumages having been thus caused. A more 
probable explanation is, that an ancient style of plumage,, 
partially modified through the transference of some 
characters from the summer plumage, has been retained 
by the adults during the winter. Finally, all the cases 
in our present class apparently depend on characters 
acquired by the adult males, having been variously 
limited in their transmission according to age, season,. 
