EVOLUTION OF THE COLORS OF BIRDS. 93 



related with the act of courtship — it being only then, in 

 fact, that the general purpose of the whole structure, as 

 well as the more special purpose of the pattern, becomes 

 revealed." Mr. Romanes also calls attention to the fact 

 that in many cases, such as the appendage of the bell- 

 bird, a very elaborate structure has been evolved which 

 is used only in courtship. Such a tube as the bell-bird's 

 inflatable tube, which is present only in the male, cer- 

 tainly could not have been developed by any excess of 

 vitality, or in accordance with any general laws of 

 growth. 



Mr. Romanes is inclined to throw aside the difficulty 

 of constancy in testhetic taste in birds a little too 

 lightly. He says: * "Although we know very little about 

 the psychology of the lower animals, we do observe in 

 many cases that small details of mental organization are 

 often wonderfully constant and uniform throughout all 

 members of a species, even where it is impossible to 

 suggest any utility as a cause." 



In commenting on the display of ornaments by male 

 birds, Mr. Wallace writes:! " But it by no means fol- 

 lows that slight differences in the shape, pattern, or 

 colors of the ornamental plumes are what lead a female 

 to give the preference to one male over another; still less 

 that all the females of a species, or the great majority of 

 them, over a wide area of country, and for many suc- 

 cessive generations, prefer exactly the same modifica- 

 tion of the color or ornament." Or to put the difficulty 

 in the words of Lloyd Morgan, I " Sexual selection of 

 preferential mating involves a standard of taste; that 

 standard has advanced from what we consider a lower 

 to what we consider a higher assthetic level, not along 



* p. 399. 



t Darwinism, p. 285. 



t Auimal Life and Intelligence, p. 205. 



