THE INSTINCT OF ANIMALS 159 



responds, as a wound-up spring responds to the 

 touch which sets it loose, are mostly beyond our 

 senses. We may form some conception of them as 

 being probably similar in character to those which 

 enable the sexes of various animals to distinguish 

 each other, and often, in certain forms to find each 

 other even when immense distances apart. These 

 stimuli are, no doubt, of various kinds. Sometimes, 

 as when one sees birds migrating south against a 

 head wind, they may be related to a highly sub- 

 limated sense of smell, or something akin to it. 

 It may be mentioned in this connection how even 

 a slight peculiar odour often serves in our own case 

 to evoke immediately and powerfully ideas and 

 emotions associated with it ; and it would seem not 

 improbable that we have in such a fact suggestion 

 of the rudimentary survival in man of a faculty 

 which has played a great part in the evolution of 

 life on a lower scale. 



One of the senses in birds and other animals 

 giving rise to remarkable results', is the sense of 

 direction. Darwin relates an incident of a horse 

 which he had sent by railway from his home 

 in Kent, over a hundred miles westward to the 

 Isle of Wight. " On the first day that I rode 

 eastward," he continues, " my horse was very 

 unwilling to return towards his stable, and he 

 several times turned round. This led me to make 

 repeated trials, and every time that I slackened the 

 reins he turned sharply round, and began to trot 

 to the eastward by a little north, which was nearly in 

 the direction of his home in Kent." Darwin con- 

 cluded that the horse knew, even at so great distance, 

 the direction in which his old home lay. Similar 



