20 iXATLJiAL HISTORY OF BIIWS. 



iiiilicnte the ancient coast-lines along which the birds originally migrated, and furtlier- 

 more, that they show the WMys by which the species immigrated into the countries 

 where they now piuss tlie summer. 



This conclusion, however, is also api)licable to the land routes C and P. The 

 geoiiiuical history of that |>art of the earth shows most conclusively that liie gieat 

 Kussian and the central Euri>iiean low-lands, during a not very distant jieriod, genlo- 

 gically Ri>eaking, were submerged, forming the bottom of a rather shallow sea, the 

 shores of which, at different times, are well indicated by the lines alluded to. Even 

 when crossing the continents, the migrating routes of marine bir<ls indicate ancient 

 coast-lines, and the immigration-road of the species inhabiting the north. We note 

 how doselv these results agree with those arrived at above, where theorizing .'ibout 

 the origin of the migrating habit. 



Having thus accounted for the theory as first jiroposed by Palmen, and nearly 

 simultaneously by Wallace, it remains to be shown how the birds are cnaljled to find 

 their wav, often thousands of miles. We need not assume a miraculous or imperative 

 instinct, nor a sixth sense, nor the intluence of terrestrial magnetism, in order to explain 

 the remarkable fact that small birds travel over large continents and vast seas twice a 

 year to and from the very spot where they were born. Practice is the mysterious 

 agent, thoutrh not only the ]iractice of the individual, but the jiractice of the species, 

 the accumulated practice of thousands of generations, originating and strengthening 

 the faculty of orientation. "It is an ascertained fact "says Wallace, "that many 

 inilividual binls return year after year to build their nests in the same spot. This 

 shows a strong local atlaclnnent, and is, in fact, the faculty of feeling, on which their 

 very existence probably depemls. For were they to wander at ran<lom each ye.'ir, 

 thev would, almost certainly, not meet with places so well suited to them, and might 

 even net into districts where they or their young would inevitably jierish. It is also 

 a curious fact that in so many cases the old birds migrate fii-st, leaving the young 

 ones behind, who follow some short time later, but do not go so far as their parents. 

 This is very strongly opposed to the notion of an imperative instinct. The old birds 

 have been before, the yoimg have not, and it is only when the old ones have all or 

 nearly all yone, that the young go too, ])robably following some of the latest stragglers. 

 They w.ander, however, almost at random, and the majority are destroyed before the 

 next spring. This is jiroved by the fact that the birds which return in spring are as 

 a rule not more numerous than those which came the j)receding s]iring, whereas 

 those which went away in autumn were two or three times as numerous. Those 

 yountr birds that do get back, however, have learnt by experience, and the next year 

 they take care to go with the >)lil ones." 



Taking into account the " inherited talent for gcogra])hy," as Weissmann ha]ipil\ 

 styles it, with which every migratory bird is born, and remembering that the birds, 

 when traveling, flv very high, and coiise(i\iently overlook a great distance of their 

 route, taking a 'bird's-eye view' of the country spread out beneath tlu'in, their 

 performance is scarcely more wonderful than is that of the pilot who safely guides the 

 vessel forhimdreds and hundreds of miles along rocky shores and islands, all of which 

 seem identical ainl inilistiniriiishable to the inexperienci-il ]iasser-l)y ; or more admir- 

 able than the infallibility with which the Itnlian fiixls his way back, even if he has 

 passed that way but once, through an endless forest of trees, which to any of us 

 seem to be absolutely alike. 



Leomiard Stejnegee. 



