still more marked in this latter phase of the migratory plieno- 

 menon." From the above passage, read in conjunction with 

 others on the altitude and velocity of the migratory flight, it 

 will be clearly evident that the author's theories on the direction 

 of the flight are based on observations made, when this migration 

 proper has been interrupted and has therefore become in the 

 light of his remarks, at any rate disturbed ; but we may fairly 

 assume that the direction is not aifected in any case. Before 

 going any further it may be as well to take a brief glance at 

 the total number of species enumerated by Herr Gatke, as 

 having occurred on the island. A convenient summary, by the 

 late Henry Seebohm, appeared in the Ibis, vol. iv., 1892, pp. 

 1-32, and will be found sufficient for the purpose. 



The total number known, or supposed to have visited 

 Heligoland, is 396 (one or two more have been added since the 

 publication of Herr Gatke's work). Of these some forty or more 

 are admitted into the list, on evidence not quite conclusive. But 

 if we remember that so many of the inhabitants of Heligoland 

 are familiar wdth all the usual visitors, we shall not err, perhaps, 

 in attaching more credence than usual in the case of these reputed 

 occurrences, especially such as have the endorsement of Herr 

 Gatke. At the same time one may be perhaps excused a feeling 

 of envy towards Aeuckens, who possesses a memory which 

 enables him, on the skin of a Warbler being submitted to his 

 notice, to declare the species of the latter identical with the 

 mutilated remains of another which passed through his hands 

 some twenty-seven years previously. Seventy-five other species 

 have been shot only once, though in a few instances other 

 examples have been reported as seen near enough for identi- 

 fication. There still remain some 280 species which pass with 

 greater or lesser regularity both in spring and autumn. A truly 

 marvellous number if Herr Gatke's theories are borne in mind, 

 and the small area under notice is not lost sight of. The 

 total European avi-Jauna, including Neartic and other stragglers, 

 amounts to, in round numbers, 600 species, so that Heligoland 

 can claim fuUy two-thirds. 



In considering Herr Gatke's theory of a rigidly preserved 

 east to west flight, it will be useful to learn what species have 



