ISOLATION or Till, MAI,K 55 



different order. But we must be.'ir in mind that 

 the process has been adjusted to meet the 

 requirements of different species : the size of the 

 territory, the period of its daily occupation, the 

 purpose which it serves these al. depend upon 

 manifold relationships and do not affect the 

 principle. Why it has been differentiated in 

 different circumstances we shall have occasion 

 to discuss later ; for the moment it is enough 

 that at the end of its migratory journey each 

 Ruff occupies one position on the meeting 

 ground. 



Now birds that are paired for life, whose 

 food-supply is not affected by alternations of 

 climate, have no occasion to desert the locality 

 wherein they have reared their offspring, and so 

 their movements, being subject to a routine 

 which would tend to become increasingly 

 definite, must in the course of time and accord- 

 ing to the law of habit formation become 

 organised into the behaviour we observe. Is it 

 necessary, therefore, to seek an explanation of 

 their tendency to remain in one place in any- 

 thing so complex as an inherited disposition ? 

 Again, since we have to confess to so very much 

 ignorance on so many points connected with the 

 whole phenomenon of migration, may there not 

 be some condition, hitherto shrouded in mystery, 

 which might place so different a complexion on 

 the corresponding aspect of migrant behaviour 

 as to rid us, in their case also, of the necessity 

 of appealing to an inherited disposition ? Such 

 questions are justifiable. And if the life- 



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