MIGRATION 



" It is well known to naturalists " (he writes) 

 " that the young cuckoo does not leave our 

 islands, and its summer haunts elsewhere, until 

 some weeks after the adult birds have left for 

 their winter home : hence parental guidance in 

 their case is not conceivable. . . . The parent 

 cuckoo deposits its eggs in the nests of other 

 birds, and the young are reared by foster parents 

 at the expense of their own offspring, which the 

 infant cuckoo soon ejects from the nest. Now, 

 these foster parents mainly belong to species 

 which do not quit our islands, or if so, do not 

 journey far : others certainly do perform consider- 

 able migrations. It matters not, however, 

 whether these foster parents are eminently mi- 

 gratory or not, for they do not accompany the 

 emigrant cuckoos on their journey to their winter 

 retreats, which lie in the equatorial regions or to 

 the south of them." 



Magnetism of the Earth. 



A somewhat ingenious suggestion — a mere sug- 

 gestion, it may be said, for there has been no 

 reasoned effort to bring it to bear on the general 

 facts of migration — is that birds may be, in some 

 way, susceptible to the magnetism of the earth, 

 and thus when crossing the sea, they are drawn 

 by some principle ot gravitation to the nearest 

 land. It has been said that Herbert Spencer's 

 only conception of a tragedy was the sight of a 

 lovely theory killed by a vicious little fact. Here 

 we have the magnetic theory done to death by one 

 of Dr. Eagle Clarke's inexorable observations. It 

 is clear that if any principle of magnetism or 

 gravitation existed, as for example, the force 

 which draws pieces of cork scattered on the sur- 

 face of water, first the smaller to the larger, and 

 eventually the whole to the sides of the vessel, 



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