604 THE DESCENT OF MAN 



cause, and transmitted in their diminished state to their male 

 offspring alone, when arrived at the corresponding age of ma- 

 tority. The belief that in the present class the male alone 

 has been modified, as far as the differences between the male 

 and the female together with her young are concerned, is 

 strongly supported by some remarkable facts recorded by 

 Mr. Blyth,' with respect to closely allied species which 

 represent each other in distinct countries. For with sev- 

 eral of these representative species the adult males have 

 undergone a certain amount of change and can be dis- 

 tinguished; the females and the young from the distinct 

 countries being indistinguishable, and therefore absolute- 

 ly unchanged. This is the case with certain Indian 

 chats (Thamnobia), with certain honey-suckers (JSTectari- 

 nia), shrikes (Tephrodornis), certain kingfishers (Tanysip- 

 tera), Kalij pheasants (Grallophasis), and tree-partridgea 

 (Arboricola). 



In some analogous cases, namely, with birds having a dif- 

 ferent summer and winter plumage, but with the two sexes 

 nearly alike, certain closely allied species can easily be dis- 

 tinguished in their summer or nuptial plumage, yet are in- 

 distinguishable in their winter as well as in their immature 

 plumage. This is the case with some of the closely allied 

 Indian wagtails or Motacillse. Mr. Swinhoe ' informs me 

 that three species of Ardeola, a genus of herons, which 

 represent one another on separate continents, are "most 

 strikingly different" when ornamented with their summer 

 plumes, but are hardly, if at all, distinguishable during the 

 winter. The young also of these three species in their im- 

 mature plumage closely resemble the adults in their winter 

 dress. This case is all the more interesting, because with 

 two other species of Ardeola both sexes retain, during the 



» See Ms admirable paper in the "Journal of the Asiatic 8oc. of Bengal," 

 Tol. xix., 1850, p. 223; see, also, Jerdon, "Birds of India," vol. i introduc- 

 tion, p. xxix. In regard to Tanysiptera, Prof. Schlegel told Mr. Blyth that he 

 could distinguish several distinct races, solely by comparing the adult males. 



• See, also, Mr. Swinhoe, in "Ibis," July, 1863, p. 131; and a previous 

 paper, with au extract from a note by Mr. Blrtb, in "Ibis," Jan. 1861, p. 25. 



