122 THE COURTSHIP OF ANIMALS 



are very playful, " their games sometimes taking the 

 form of a tilting match. Three take part ; two sit on 

 convenient twigs facing one another, and the third, from 

 the central position, might almost be called an umpire. 

 Numbers One and Two lower their heads, each in antici- 

 pation of the other moving ; one of them, call him Number 

 One, then springs into the air and darts at Number Two : 

 Number Two dodges and occupies the position vacated 

 by Number One ; each of them then faces round ready 

 to continue the fray, the change of positions becoming 

 quite rapid." But no recurrence of these antics has been 

 noted during the course of the adult sexual display, which 

 is confined to posturing and displaying the outspread 

 wings and tail. Nevertheless there can be no doubt 

 but that such games in later life are incorporated, in 

 the case of many species, with the love display. 



That the reproductive glands have played, and still 

 play, a by no means unimportant r61e in Evolution is 

 shown by the history of the secondary sexual characters. 

 Among the birds, at any rate, the early stages of physical 

 changes belonging to this " figuration " are to be seen in 

 various forms of posturing, which in their more elaborate 

 developments we call " dances." In many cases, as for 

 example among the Warblers, the periods of sex-emotion 

 are marked by posturing alone. But in a number of 

 species, as has already been shown, the products of the 

 sexual gland seem to have undergone some furthei 

 elaboration which has resulted in the additional phenomena 

 of gaudy coloration, in hypertrophied plumes, and in 

 weapons of offence. 



But not yet is the list of such sexual products 

 exhausted, for no mention has so far been made of the 

 development of the many wonderful devices for the 



