254 CARNEGIE INSTITUTION 



unsuspected direction through the interior of the continent, and he 

 also indicated the routes of other species in a tentative way. 



Pressure of other work, as well as lack of material, has prevented 

 further research in that direction, and no one else has taken up the 

 subject or is liable to do so. A year ago, however, he was led to 

 investigate the routes of an Old World migrating bird which ex- 

 tends its range into Greenland and eastern North America on the 

 one side and into Alaska on the other. He was able to prove that 

 the bird in these two localities is represented by two subspecies, one 

 of which migrates in winter to western Africa, the other to India. 

 The routes thus traced clearl}' indicated the way by which the 

 species originally invaded America. To better illustrate the im- 

 portance of the investigation we may be permitted to quote the 

 concluding paragraph of the generalization based upon it, as follows : 



' ' It seems that one more lesson can fairly be drawn from the 

 diiterentiation of the Greenland race, viz., that the Greeuland- 

 Iceland-England route must be considerably older than the Alaska- 

 Chukchi-Udski route, since it has resulted in the establishment of 

 a separable race. A consideration of the further fact that no regu- 

 lar migration route could have been effected between Greenland, 

 Iceland, and Great Britain during the present distribution of land 

 and water in that part of the world also leads us back to a period 

 when the stretches of ocean now separating those islands were more 

 or less bridged over b}- land. For such a condition of affairs we 

 shall have to look toward the beginning of the Glacial period. At 

 that time it must, therefore, be assumed that the Wheatear extended 

 its range into Greenland. The advent of the typical form into 

 Alaska, on the other hand, is probabh^ one of very recent time, an 

 assumption corroborated by the somewhat uncertain and erratic 

 distribution of the species in that northwestern corner of our conti- 

 nent." (Proc. U. S. Nat. Mus., XXIII, 1901, p. 477.) 



The exceptionally satisfactory results of this investigation were 

 due to the coincidence of a fairly good series of specimens in the 

 National Museum with the fact that the difference between the two 

 races was one of length of wing, and that consequently the meas- 

 urements by European authors could be utilized. If the distin- 

 guishing characters had been of a different nature, the material at 

 hand would have been insufficient. 



It will thus be easily seen that if we had the material we could 

 determine these routes for many species, and thus secure valuable 

 facts for a correct interpretation of many of the most important 

 problems now under discussion. 



