BIRDS. 567 



the females have come to differ chiefly from partaking 

 more or less of the characters thus acquired by the males. 

 The effects, moreover, of the definite action of the condi- 

 tions of life will not have been masked in the females as 

 in the males by the accumulation through sexual selection 

 of strongly pronounced colors and other ornaments. The 

 individuals of both sexes, however affected, will have been 

 kept at each successive period nearly uniform by the free 

 intercrossing of many individuals. 



With species in which the sexes differ in color it is possi- 

 ble or probable that some of the successive variations often 

 tended to be transmitted equally to both sexes; but that 

 when this occurred the females were prevented from acquir- 

 ing the bright colors of the males by the destruction which 

 they suffered during incubation. There is no evidence 

 that it is possible by natural selection to convert one form 

 of transmission into another. But there would not be the 

 least difficulty in rendering a female dull-colored, the male 

 being still kept bright-colored, by the selection of suc- 

 cessive variations which were from the first limited in their 

 transmission to the same sex. Whether the females of" 

 many species have actually been thus modified must at 

 present remain doubtful. When, through the law of the 

 equal transmission of characters to both sexes, the females 

 were rendered as conspicuously colored as the males, their 

 instincts appear often to have been modified so that they 

 were led to build domed or concealed nests. 



In one small and curious class of cases the characters 

 and habits of the two sexes have been completely trans- 

 posed, for the females are larger, stronger, more vociferous 

 and brighter colored than the males. They have also be- 

 come so quarrelsome that they often fight together for the 

 possession of the males like the males of other pugnacious 

 species for the possession of the females. If, as seems 

 probable, such females habitually drive aways their rivals, 

 and by the display of their bright colors or other charms 

 endeavor to attract the males, we can understand how it is 

 that they have gradually been rendered by sexual selection 

 and sexually limited transmission more beautiful than the 

 males the latter being left unmodified or only slightly 

 modified. 



Whenever the law of inheritance at corresponding ages 



