22 DISPOSITION TO SECURE A TERRITORY 



necessary physiological condition must arise at 

 an early stage in the cycle of events which 

 follow one another in ordered sequence and 

 make towards the goal of reproduction, and that 

 the behaviour to which it leads must be one of 

 the earliest visible manifestations of the seasonal 

 development of the sexual instinct. When does 

 this seasonal development occur ? For how 

 long does the instinct lie dormant ? In some 

 species there is evidence of this first step in the 

 process of reproduction early in February ; there 

 is reason to believe that in others the latter part 

 of January is the period of revival ; and the 

 possibility must not be overlooked of still earlier 

 awakenings, marked with little definiteness, 

 though nevertheless of sufficient strength to call 

 into functional activity the primary impulse in 

 the sexual cycle. Here, then, we meet with a 

 difficulty so far as direct observation is con- 

 cerned, for the duration of the period of 

 dormancy and the precise date of revival vary 

 in different species ; and, if accurate information 

 is to be obtained, the study of the series of 

 events which culminate in the attainment 

 of reproduction ought certainly to begin the 

 moment behaviour is influenced by the internal 

 changes, whatever they may be, which are 

 responsible for the awakening of the sexual 

 instinct. 



In considering how this difficulty might be 

 met, the importance of migratory species as a 

 channel of information was gradually borne in 

 upon me ; for it seemed that the definiteness 



