2A.± CoL-ES, Gaffe's HcUgolaud. foct^ 



the superfluous extent of strenuously insisting upon them in 

 print. He files a general caveat we shall do well to heed. 

 Isepipteses and magnetic meridians, coast-lines and river- 

 channels, food-supply and sex-impulses, hunger and love, hom- 

 ing instincts and inherited or acquired memory, thermometer, 

 barometer and hygrometer, may all be factors in the problem, 

 good as far as they function ; but none of them, and not all such 

 together, can satisfy the whole equation. The subject has engaged 

 the attention of many able writers ; but the very excellence of 

 Giitke's contribution to the scientific aspects of the case certifies 

 that he has not said the last word, for it is sure to stimulate 

 further research and excite renewed discussion. He devotes a 

 chapter to each one of the following subjects : The course of 

 migration generally in Heligoland ; direction of the migration 

 fiight; altitude of the migration flight; velocity of the migration 

 flight ; meteorological conditions which influence migration ; 

 order of migration according to sex and age ; exceptional migra- 

 tion phenomena ; what guides birds during their migrations ; and 

 finally, the cause of the migratory movement. To go into any 

 particulars here would be to slight others equally interesting and 

 often equally surprising; but some points may be merely 

 mentioned. Instead of north and south movements in all cases, 

 there are some east and west, at right angles with meridians, 

 independent of coast-lines. Instead of the thousands of migrants 

 we may see, or the hundreds of thousands we may estimate, we 

 are told of the millions and billions — such incalculable myriads 

 flying past a single rock that all the destruction human agency 

 could effect in all time would be inappreciable. Some of the 

 distances, altitudes, and velocities of which migrating birds are 

 proved to be capable would be incredible were they not so 

 well attested : and such capacities for flight are shown in some 

 instances of birds we are not accustomed to consider very good 

 fliers. Meteorological conditions influence migration more pro- 

 foundly than we commonly suppose ; the alternation of day 

 and night has some unsuspected effects. Birds are really better 

 weather-prophets than our official ' forecasters ' always show 

 themselves to be, if not quite as good as the Roman haruspices 

 suppo-sed avian augury was. Birds in the water can in some 



