218 SEXUAL selection: birds. Part II. 



waders. Lastly, in regard to the young differing 

 greatly from botli sexes in their adult summer and 

 winter plumages, this occurs with some herons and 

 egrets of North America and India, — the young alone 

 beino^ white. 



I will make only a few remarks on these complicated 

 cases. When the young resemble the female in her 

 summer dress, or tlie 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 difQcult 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 tliis 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, 



