MIND AND MEMOnr OF BIRDS. 25 



think, that the hereditary memory is growing 

 weaker year by year, and that the time may 

 come when migration will cease. In many 

 cases the need for migration does not exist, 

 therefore the desire is merely traditionary, as 

 it were, and must be fading out. The mock- 

 ing-bird's habit is an instance of the imperfect 

 migratory memopy. Why should a few of 

 this species come as far north as the Ohio 

 valley to nest when the great body of them 

 are happy to remain far south? Such a ques- 

 tion might be asked regarding many other 

 species. The answer is to be found in trans- 

 mitted memory and hereditary desire. 



