MIGKATIONS OF BIRDS. 297 



foregoing remarks, that the direction taken by the migrations of 

 flying animals is, in a great measure, determined by the direction 

 of the winds ; without this, Wallace's explanation would remain 

 as unsatisfactory as the hypothesis of the sunken Atlantis. Such 

 effects ought, as we may suppose, to be most easily recognisable in 

 the migration of those flyers which of their own free will make 

 long migratory and aerial journeys ; moreover, we might expect 

 to find some reliable data in observations made on migratory 

 birds. But, strangely enough, all the investigators of the 

 phenomena of migration in birds appear to have taken no 

 notice of this matter ; my closest researches have failed to find 

 any data with regard to it, and the only remark which may 

 have some value is that of Von Brehm, that migratory birds al- 

 ways fly against the wind. The necessity for this is self-evident ; 

 a bird which is driven before even a moderately strong wind 

 blowing through its feathers, is prevented flying, and still more 

 hindered in steering. Even in the most recent and very 

 thorough researches as to the phenomena of the migrations of 

 birds by Von Palm6n,"* this point is wholly disregarded, and 

 though it must be admitted that several of the lines of migration 

 laid down by him from many observations can by no means 

 be brought into agreement with those of prevailing winds, on 

 the other hand the number of cases is not small in which a 

 very extensive agreement between the two is conspicuous ; this 

 is the case, to cite a single example, in the west of Europe. 



If then the observations at our disposal afford no satis- 

 factory information as to the question how far the influence, 

 certainly exerted by tlie wind, affects migratory animals, it 

 is still more difficult to trace its effects on aquatic animals, 

 notwithstanding that they undoubtedly come under its in- 

 fluence. This influence can naturally only be effective in two 

 ways, either by flying creatures, like water-birds, carrying 

 small animals or eggs on their journeys with them, clinging to 

 their feet, or by the wind transporting these aquatic creatures 

 directly through the air. Darwin has pointed out the possi- 

 bility of the first mode in his discussion on the geographical 

 distribution of fresh-water mollusca, particulai'ly with a view to 

 explaining the fact, recognised by him, that these animals, 



14 



