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Show 190 SEXUAL SELECTION: BIRDS. PART II. 1 ble facts recorded b Y Mr .. Bl Yt h ' s with respe.c t rt·eom~:::1y-allied species which represent each other m distinct countri.e s. For w·i t 11 sevei..a 1 of these represe.n.- ~:1~v=~~:~~eso:hceh::;!t a:~l~::~:e. d~~1:;~~~1::; ct~~ .!' 1 d the young being undistmgmshable, a~d ltehmerae feosr ea nab solutelv unchange a· Th. is the case Wlth IS • . ain Indian chats (Thamnobia), with cer~am ho~e~- ~~~ters (Nectarinia), shrikes .~Tephrodorms), .~~~.~ kingfishers (Tanysiptera), Kall~J pheasants (G, p sis) and tree-partridges (Arboncola). . In some analogous cases, namely with birds .h:v~~g a distinct summer and winter plumage, bu~ wit . e two sexes near· ly alike ' ce.r tain .c losely-allied. speci·e s 'ly be distinguished m thmr summer OI nuptia1 can eas1 · h · · t l ge Yet are undistinguishable m t eir wm er as Pwuelml aas i'n their immature plumage. Tlu's .I·s the case with some of the closely-allied Indian wag-tails or ~ota- '11 Mr· Swinhoe s informs me that three speCies of Cl ro. . . h th . A rcLJ eO 1a , a genus· of herons ' whiCh rep.r e.s ent eda'c o er .{![! t " on separat e co Dt.Inents ' are " most stnkmgly Iueren when ornamented with their sum~ner plu~es, ~ut r~re 1l ai· dl y, I· r a t all ' distinot>· uishable dunng• theh w. mt.e r. tI he y.o ung a1 s o of these three species m t. eirh I·m ma· ut re p 1u mag e closely resemble the adul. ts m t· en· b wm er dress. This case is all the more mterestmg eca~se with two other species of Ardeola both sexes retam, during the winter and summer, nearly the same plum- • Sec his atlmirablc paper iu the 'Journal of .the Asiati~ ~oc. o_f Bcn"al,' vol. xix. 1850, p. 223; sec also J ordon, 'Buds of Indm, vol. ~· · t od ct'ton p ·xxix In regrtrd to Tany:siptcra, Prof. Schlegel told m1\' Irr. om uy th th' at· he •c ·o uld distingm.s h several d1· sh· nct m. cc,s , so 1e 1Y by comparing the rtuult mrtles. . , . a See nlso 1\fr Swinhoc, in 'Ibis,' July, 1863, p. 131 ; and a piC\ wu::; paper, with an ~xtro.ct from a note by Mr. Blyth, in' Ibis,' Jan. 1861, p.5~ . CJJAl'. X\'l. THE YOUNG LlliE 'l'IIE ADULT FEMALES. 191 age as that possessed by the three :first species during the winter and in their immature state; and this plumage, which is common to several distinct species at different ages and seasons, probably shews us how the progenitor of the genus was coloured. In all these cases, the nnptial plumage which we may assume was originally acquired by the adult males during the breeding- season, and transmitted to the adults of both sexes at the corresponding season, has been modified, whilst the winter and immature plumages have been left unchanged. The question naturally adses, how is it that in these latter cases the winter plumage of both sexes, and in the former cases the plumage of the adult females, as well as the immature plumage of the young, have not been at all affected. ? ~rhe species which represent each other in distinct countries will almost always have been exposed to somewhat different conditions, but we can hardly attribute the modification of the plumage in the males alone to this action, seeing that the females and the young, though similarly exposed, havenot been affected. Hardly any fact in nature shews us more clearly how subordinate in importance is the direct action of the conditions of life, in comparison with the accumulation through selection of indefinite variations, than the surprising difference between the sexes of many birds; for both sexes must have consumed the same food and have been exposed to the same climate. N everthe1ess we are not precluded from believing that in tho course of time new conditions may produce some direct effect; we see only that this is subordinate in importance to the accumulated results of selection. vVhen, however, a species migrates into a new r.ountry, and this must precede the formation of representative species, the changed conditions to which |