MIGRATION. 289 



decreased temperature of the earth and water, may all have 

 their influence." 



It will be observed that this theory, besides being intrin- 

 sically probable, derives a good deal of support from the 

 enquiries made by Mr. Darwin, which have shown that there 

 is a general relationship between oceanic islands which there 

 is independent reason to conclude have never been joined to 

 the mainland, and an absence of migratory birds.* 



It will also be observed this theory makes two important 

 assumptions — first, that the birds have a very accurate sense 

 of direction, and second, that a no less accurate knowledge of 

 the particular direction to be pursued is inherited ; for it is 

 certain that the young Cuckoo (which leaves England after 

 its parents) cannot be guided on its first journey by any other 

 means, and it is asserted that the same is true of the young 

 of many other species.t Taking then these assumptions 

 separately, the first is no more than a statement of fact, un- 

 accountable though the fact may be. That is to say, a very 

 accurate sense of direction migratory birds unquestionably 

 possess, and it is probably the same in kind as the so-called 

 " homing " faculty which is shown by many domesticated 

 animals, and also, as Mr. Darwin points out, by savage man. 

 I could till pages with letters which I have received from 

 all parts of the world describing more or less remarkable 

 cases of the display of this faculty by dogs, cats, horses. J 



* To he quit'- fair, however, I must here allude to the only fact I have 



iri''t wit 1 1 which Menu to d pposed to this theory. Mr. Hindis in his 



work entitled The Naturalist in Bermuda, observes thai the migratory golden 

 plover {Charadriui marmoratus) passes over the inlands in countless multi- 

 tudes (hut wit 1 1 « » 1 1 1 ever alighting) on the journey south, while they are never 

 seen passing over the islands on their return journey north. Now, if it is a 



fait that the two journey* are taken hy dillerent routes, a difficulty would ho 

 encountered hy the ahove theory ; hid as Mr. llunii- mii s that the birds fly 



at an enormoui height while passing over the islands on their southern 



journey, it is not, I think, impossible that thej may take the same route on 



their northern journey, although at a still higher elevation, ami thus escape 



notice. 



t See Temminck, M<n>. <FOm., ed, 2, iii, Introd., p. x 1 i i i , and Beebohm, 

 Bibt ria fa "Europe. ( >n the other hand Leroj ->ay - that in the case of swallows 

 "those who have had no instruction do not migrate, and the young birds 

 sen to be led by those whose age and experience give them know!. 



and authority ; ' and adds that if a hrood are hatched out too late to neeoin- 



panj t In' old birds m their migration, "it is in vain t hat thej reach maturity 

 the\ perish the victims of their ignorance, and of the tardy birth 

 which mad'- them unable to follow their parents" {/,„-. eit., pp. L88— 4). 



J 1 have one insfaWlOS of a cat. returning in four days from London to 



