102 CALIFORNIA ACADEMY OF SCIENCES. 



of the brilliant colors and plumes of male birds they are 

 as follows: Katabolism of the male supplies a surplus 

 of energy to be expended (Geddes and Thomson); some 

 color must be present in birds as in all objects, and its 

 distribution is limited (but not determined) by the 

 nature of the integument and the general laws of growth 

 (Wallace); birds and some insects (?) have a visual 

 apparatus which is sensitive to contrasts of color and is 

 more easily fatigued by certain shades and patterns than 

 by others, and consequently certain combinations are 

 more pleasing than others; the female bird (generally) 

 chooses a mate from among a number of suitors, con- 

 forming to what is more or less pleasing or disagreeable 

 in the plumage of the males (Darwin); owing to the 

 surplus of males, the conspicuous plumes and colors 

 which are thus developed by the choice of the female 

 bird, are a positive advantage to the species, reducing 

 the numbers of the predominant sex, and their preser- 

 vation is thus insured by natural selection (Stolzmann); 

 in many cases the female bird inherits the bright colors 

 of the male, but these colors are more frequently sup- 

 pressed by the action of natural selection, from the 

 greater necessity for protection on the part of the female 

 during the process of incubation (Wallace). 



According to the view thus summed up, each one of 

 the investigators who have contributed to the subject 

 have presented only a portion of the truth and have 

 attempted to make it stand for the whole. This synthe- 

 sis seems to satisfy all the various objections which have 

 been raised against sexual selection, and to supply a tol- 

 erably complete explanation of secondary sexual char- 

 acters in birds. 



