J^TRDS. 566 



differently from wtat occurs in Class I, Lave transmitted their colors 

 to their male offspring at an earlier age than that at which they were 

 first acquired; for, if the males had varied while quite young, their 

 characters would probably have been transmitted to both sexes.* 



In Aithurus polytmus, a humming-bird, the male is splendidly 

 colored black and green, and two of the tail-feathers are immensely 

 lengthened; the female has an ordinary tail and inconspicuous 

 colors; now the young males, instead of resembling the adult 

 female, in accordance with the common rule, begin from the first to 

 assume the colors proper to their sex, and their tail-feathers soon 

 become elongated. I owe this information to Mr. Gould, who has 

 given me the following more striking and as yet unpublished case. 

 Two humming-birds belonging to the genus Eustephanus, both 

 beautifully colored, inhabit the small island of Juan Fernandez, and 

 have always been ranked as specifically distinct. But it has lately 

 been ascertained that the one which is of a rich chestnut-brown 

 color with a golden-red head, is the male, while the other, which is 

 elegantly variegated with green and white, with a metallic green 

 head, is the female. Now the young from the first somewhat resem- 

 ble the adults of the corresponding sex, the resemblance gradually 

 becoming more and more complete. 



In considering this last case, if as before we take the plumage of 

 the young as our guide, it would appear that both sexes have been 

 rendered beautiful independently; and not that one sex has partially 

 transferred its beauty to the other. The male apparently has 

 acquired his bright colors through sexual selection in the same 

 manner as, for instance, the peacock or pheasant in our first class of 

 cases; and the female in the same manner as the female Rhynchaea 

 or Turnix in our second class of cases. But there is much difficulty 

 in understanding how this could have been effected at the same time 

 with the two sexes of the same species. Mr. Salvin states, as we 

 have seen in the eighth chapter, that with certain humming-birds 

 the males greatly exceed the females in number, while with other 

 species inhabiting the same country the females greatly exceed the 

 males. If, then, we might assume that during some former length- 

 ened period the males of the Juan Fernandez species had greatly 

 exceeded the females in number, but that during another lengthened 

 period the females had far exceeded the males, we could understand 

 how the males at one time, and the females at another, might have 

 been rendered beautiful by the selection of the brighter-colored 

 individuals of either sex; both sexes transmitting their characters to 

 their young at a rather earlier age than usual. Whether this is the 

 true explanation I will not pretend to say ; but the case is too remark- 

 able to be passed over without notice. 



The following additional cases may be mentioned: the young males of 



females (Audubon, 

 nestlings of a blue 



. , . of India," vol. i, p. 



389). Mr. Blyth also informs me that the sexes of the stonechat, <Saxicota itibi- 

 cola, are distmguishable at a very early age. Mr. Salvin giv<^s (" Proc. Zoolog. 

 Soc.," 1870, p. 206), the case of a humming-bird, like the following one of 

 Eustephanus. 



^ luc luiiuwiug auuitioiiai uases uiay ue uieiiLioiieu: m 

 Tanagra inibra can be distinguished from the young f 

 " Ornith. Biography,*' vol. iv, p. 31)2), and so it is within the 

 nuthatch, iJendiophila froniahs, of India (Jerdon, " Birds c 



