MIGRATION OF MAMMALS MATTHEWS 283 



it is, and of where it is going — that is to say it must have some kind 

 of geographical knowledge and some kind of mental image that cor- 

 responds to a map. If it had this knowledge, it is conceivable that 

 the altitude of the sun might give it some rough idea of its latitude 

 on its mental map. But it seems to me quite impossible that it would 

 in any way be able to determine its longitude, however roughly. I 

 do not suggest, of course, that an animal would have any conscious 

 conception of these coordinates, but fixing a position on a map of any 

 sort implies the use of them, even if it is unconscious. Furthermore, 

 any suggestion of navigation implies the knowledge of a destination 

 and of its approximate position ; it seems to me very improbable that 

 any animal can have that knowledge. And some animals that migrate 

 singly and alone certainly cannot have it, for instance the young of 

 some birds that migi'ate over routes they have never traveled, to 

 places they have never visited, long after their parents have deserted 

 them. 



We know that some insects orientate themselves by the position of 

 the sun, and that they can do so even when the sun is obscured by 

 cloud because they are sensitive to the polarized light impinging on 

 them. But this orientation serves only to take them to and fro be- 

 tween home and foraging grounds that they have discovered by ran- 

 dom search; an experience, if not a knowledge, of both ends of the 

 journey is implied, and the distances covered are furlongs at most, 

 not thousands of miles. It seems to me improbable that migrating 

 mammals can be guided by such means. 



It is of course possible that migratory animals have some sense of 

 direction that we have not. The way in which cats and dogs, and some 

 kinds of birds, sometimes return to their homes over great distances 

 after they have been removed in closed containers so that they can 

 have no possible guidance from a memory of the route traveled, lends 

 some support to this suggestion. If animals do have a perception that 

 is lacking in ourselves, we can no more hope to understand it than a 

 man blind from birth can understand what is meant by "color." But 

 a sense of direction would presumably need some sense organ for the 

 reception of stimuli of some sort — no animal can be aware of its en- 

 viroimaent, or even of itself, without the appropriate receptor organs. 

 No such receptors are known to us. It is possible, but not probable, 

 that animals do have receptors of this nature and that we do not 

 recognize them — lacking that sense we overlook them. 



Have we any remains of a sense of direction that might have been 

 more highly developed in our remote ancestors? It seems improbable 

 that we have any idea of direction if we are cut off from all visual or 

 other perception of the route we have traveled. Of course, if you were 

 carried blindfold to the middle of England and told to make your way 

 across country to London you might succeed in hitting it off roughly 



