154 THE COURTSHIP OF ANIMALS 



recent years show that the theory of Sexual Selection, as 

 Darwin propounded it, especially in so far as birds are 

 concerned, is no longer tenable : but it is not an exploded 

 theory, it has only undergone modification. So far as the 

 evidence goes, it would seem that the first of the series 

 of events in the sexual cycle is performed by the already 

 avid male, when he proceeds to secure a " territory " 

 large enough for his needs. In insectivorous and car- 

 nivorous species this area is fairly extensive. .No other 

 male will be allowed within its confines. The perfection 

 of this instinct is vitally important, if sufficient food for 

 the offspring that are to be is to be assured. Where 

 the food is inexhaustible, as with the Auk-tribe, only a 

 ledge large enough to hold the egg is required. Only 

 avid males will develop and respond to this stimulus. 

 The second stage occurs with the arrival of a female 

 in the area. She does not at once proceed to " select " 

 her mate, passing on if he fails to provoke her admira- 

 tion. Her sexual condition is apparently as yet but half 

 awakened : to rouse this, the male supplies an aphrodisiac 

 in some form of display to which, in the normal course 

 of things, she responds, often also with some form of 

 display, or indication of the desire which has been aroused. 

 The intensity of the performance seems to vary with the 

 intensity of the sexual passion, which appears to be greater 

 in some species than others, and especially so with such 

 as have conspicuously ornamental plumage. There is, 

 indeed, a variation in the sexual appetite as there is in 

 the ornamentation. The two are reciprocal, and are 

 determined in degree by the stimulatory qualities of the 

 hormones of the sexual glands. Where these have been 

 developed in like intensity by the females, they also 

 display. Diminution in the quality and quantity of the 



