ROUTES OF MIGRATION. m 



to the tundras of Northern Europe or Asia probably 

 follows all in turn. It has an experience of Valley 

 Routes in the Nile, the Don, the Volga, and the 

 Petchora ; of Sea Routes across the Mediterranean 

 by way of Cyprus or Candia, and the Greek 

 Archipelago ; of Coast Routes along the shores of 

 the Black Sea ; and probably of Mountain Routes 

 in the Caucasus — each and all of which long ages 

 of accumulated experience have taught that species 

 to make the fullest use. Some of these routes are 

 much more direct than others ; many are exces- 

 sively circuitous, and vividly illustrate the gradual 

 way in which a species has spread from a centre 

 of dispersal, turned this way and that by endless 

 conflicting influences in the unceasing struggle 

 for place and for life. Here a desert stopped the 

 w^ay, and a fly-line to avoid it had slowly to be 

 learnt ; there some other dominant and vigorous 

 species already held the ground, causing a detour 

 •or even a retreat ; here a mountain pass led to 

 new areas of dispersal, and fields for Emigration ; 

 there conditions of life peremptorily forbade settle- 

 ment or increase — all this and more is indelibly 

 stamped upon the present fly-lines of every species, 

 had we only perceptive power enough to decipher 

 it. For, depend upon it, these tortuous Routes of 

 Migration are the hieroglyphics which record the 

 Line of Emigration followed by species in past 

 ages, and unquestionably demonstrate the only 

 feasible way in which the road has been learnt ! 



