12 ANNALS OF SCOTTISH NATURAL HISTORY 



actual routes and passages on their migrations one area 

 with another, and each with each. Such investigations have 

 already led up to conclusions regarding the phenomena of 

 the dispersal of species, and also to some knowledge of their 

 possible, probable, or certain original headquarters. (The 

 latter point, of course, is arrived at by a comparison with 

 distribution and statistics outside our presently treated of 

 areas, by the observations of Continental naturalists, or of 

 personal observations conducted and recorded by the travelled 

 naturalists of our own country abroad, etc.) 



Another step in the right direction, and with the same 

 ends in view, has been initiated by the British Association's 

 " Committee on the Migration of Birds " at lighthouses, as 

 shown by the nine reports published between 1879 and 

 1887 inclusive, and the digest of these published in 1896, 

 worked over again from the whole of the original schedules 



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by the unbiassed work of Mr. Eagle Clarke, and delivered 

 at the British Association Meeting at Liverpool in that 

 year. 



Yet another step has been taken, still with the same 

 ends in view, viz. : by a treatment of single species both as 

 regards past and present distribution, by calling in the 

 assistance of the earliest records of appearances, by 

 mapping these under a series of chronological dates, and (so 

 far as such a method can be relied upon) by tracing out the 

 various " avenues of advance " along " the lines of least 



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resistance " or " greatest facilities " resultant upon the "natural 

 increase of species " and " overflows from congested districts 

 and centres." 



To illustrate the facts from as many standpoints as 

 possible has been among my first cares in contributing 

 material. I have tried to select examples under very differ- 

 ent circumstances as attached to the history of each. 



I may be allowed to attempt to further illustrate this by 

 placing my examples in juxtaposition. 



First, I selected the Capercaillie l as an example. This 

 giant grouse became extinct in Britain ; but after a restora- 

 tion at Taymouth and at several other centres of introduction, 

 dispersed over large areas of suitable country along certain 

 1 " The Capercaillie in Scotland." (Edinburgh: David Douglas, 1879.) 



