CONDITION ACCOMPANYING CHANGE 241 



between different species, the more so since 

 the biological end of securing a mate is 

 definitely excluded. And we have something 

 in the nature of proof of the correctness of 

 this view in the fact that she accompanies her 

 mate when he joins the flock, and that there 

 his instinct is not susceptible to stimulation. 

 We then proceeded to examine certain cases 

 in which all the indications pointed to the fact 

 that the " will to fight " was present in only 

 one of the opponents ; and we attached consider- 

 able importance to this circumstance, because 

 we knew from experience that the same bird 

 which seemed to lack courage, could at other 

 times and in other situations be most aggressive. 

 If then we ask what condition was present on 

 the one occasion that was absent on the other, 

 we have no difficulty in finding a reply — on 

 every occasion on which the opponents appeared 

 to be unevenly matched, one was in occupation 

 of a territory and the other was not. And if 

 we inquire further as to which of the two was 

 the aggressor, the answer is again clear, namely, 

 the bird that occupied a territory. Finally we 

 considered some particular instances in which 

 the "will to fight" was present alike in both 

 opponents, and in which the battles were 

 protracted and severe. 



But the fact that a bird has established a 

 territory is not in itself sufficient to render its 

 hostile nature susceptible ; it must be actually 

 in occupation if a response is to be elicited. 

 We reach this conclusion step by step : the 



