REPOiri' ox IHi: MKa.'ATION OF BIK1>S. 379 



Tlu' order of iiii.urarion of the iiidniduals iiia_\' !)»■ icdnced to two 

 simple types: (1) wlieiv a miiiiht'i' of individuals move from one place 

 to aiiotlier without <lianjiiii<;' their relative i»ositious (uaclieiuauder- 

 zug); (2) where the relative positions are chaMu'ed, some moving- more 

 rapidly than others (voriihei'-zug): with all transitions between the 

 two. 



The irregular migrations also are to be distinguished from the regu- 

 lar, and the stray visitors are to be considered in harmony with this 

 princii)le. These stray visitors can essentially contribute in the spring 

 in different ways to the extension of the breeding district. 



Theoretically the origin of the migration instinct beconu's somewhat 

 more comprehensible tlian before; and the explanations found might 

 be fit to cause a new discussion alxait the phenomenon of migration. 

 This conception of the )>articulars of the migrations met with appro- 

 val on nniny sides. Nevertheless the voice of ,Mr. E. F. von Ilomeyer 

 was soon raised against it, from whose work ( />/f' Wditdcnnu/cii dcr 

 Vogel, ISSl) 1 lune l)rought together tlie following lea-ding views:* 



Birds usually migrate in a fixed direction, — in the greater part of 

 Europe essentially from northeast to south-west. The maintenance of 

 this direction de])ends on the birds' sense of direction. 



The i)assage of a i)articular si)ecies extends over every single point 

 within its migration district; for the birds fly so high in the air that 

 the direction of their liight becomes independent of the topogra])hy of 

 the ground. From this height they perceive suital)le resting places, 

 where they can repose or stop. J>y combining such i>laces, the pre- 

 tended migration routes are constructed, which by no means correspond 

 to the facts. The birds do Jiot move along linear routes, at least not 

 along coast ways. They move with an extended front, everywhere. 



(July in isolated places are the l)irds compelled ])y in.surmountable 

 obstacles, lik«' high mountains, to deviate from the general direction, 

 and to collect together in larger numbers at one point than at another, 



The erroneously so called stray visitors have by no means gone 

 astray. They are simply rare birds, which, owing to the inconijth'te- 

 ness of the obseivations, are overlooked in most ])laces. 



All theoretical speculations (m the migration are to be r<je(;ted. 

 Tlu'y are not only useless, but directly injurious: because they oidy 

 forestall the real observation of nature, and, instead of adv'ancing 

 knowledge, merely oi>en the door to fancy. The tendency to construct 

 hypothetical migration routes for the birds has sprung from the now 

 l)opidar endeavor to trace everything back to the Darwinian doctrine. 



In later years llaitwig ibllowed E. \'on llomeyers conception of the 

 course of the migration {Jonni. f. Ornlth.. bSSo, ]>. 127: comi)arealsoHar- 

 tert, J.f. Ornith., 1887, p. ^ol and 1889, [). 234). 



The writer had already in the year 1882 published his "answer" to 



* This is done with all reservation, for there are still isolated places in the work 

 where the above views, formerly snbscribed by the author named, are still held. 



