Vol i80 11 ] Allen, Gatke's 'Heligoland: 1 47 



shore birds, the adults precede the young in the autumnal 

 migration. 



In Chapter VII (pp. 1 14-130), under the head of k Excep- 

 tional Migration Phenomena,' are grouped many facts of interest 

 respecting the season and character of occurrence and sources 

 of origin of the numerous waifs and strays, or chance visitors, 

 which have been taken or observed on Heligoland. 



Chapter VIII (pp. 131- 142) is devoted to a consideration 

 of the question ' What Guides Birds during their Migrations ? ' 

 and Chapter IX (pp. 143-148) to 'The Cause of the Migra- 

 tory Movement.' These are principally made up of destructive 

 criticism of the theories and suggestions of previous writers, his 

 conclusion being that the former question "presents to the 

 savants of our day as great a riddle as it did to the first ob- 

 server in ages before the dawn of history " (p. 132).' He con- 

 cludes Chapter VIII by saying: "Having thus examined the 

 many various attempts made to explain the wonderful faculty 

 possessed by migrants of discovering the right path of their 

 migration, and shown how insufficient most of them are when 

 confronted with actual facts, observed directly in nature, in the 

 course of more than fifty years' investigations and at a spot so 

 favoured as Heligoland, I cannot say that I feel encouraged to 

 add further to the number of such attempts by others of my 

 own" (p. 142). As he has during the previous chapters advanced 

 theories of his own to explain the various phenomena of migra- 

 tion, usually in direct opposition to those of other students of 

 the subject, and has not hesitated to reject as not worth con- 

 sidering observations made elsewhere if they do not tally with 

 his "fifty years' investigations" on his "favoured little isle of 

 Heligoland," it seems almost remarkable that he should content 

 himself in the present case — after proving (to his own satis- 

 faction) everybody else wrong — with this modest confession of 

 inability to explain this old-time riddle. He discards the idea 

 of definite routes of migration ; of topographic features of the 

 landscape, — coast lines, river courses, and mountain chains, — 

 serving as landmarks ; and discredits the possibility of a heredi- 

 tary transmission of knowledge derived from experience. He 

 erroneously assumes that because birds migrate principally by 



