THE NATURALIST'S VISION 357 



song, the method of expression of such a song is 

 largely derived by hearing during its infancy the 

 song of the male parent, it being nearer and more 

 readily noticed. 



I cannot but allude to the factor of adaptability, 

 and its bearing on the domestication of animals. 

 One reason, and perhaps the greatest one for our 

 limited number of domesticated animals, is the lack 

 of adaptability and plasticity together with that 

 of docility among wild forms. Hence only those 

 most readily dealt with have been utilized. It is 

 probable that among the many kinds still untried 

 valuable forms might be domesticated. Here 

 is evidently one field of economic value. An- 

 other economic field has been developed among 

 animals even lower than birds; so that it does 

 not seem visionary to suggest the possibility 

 of re-stocking some of the depopulated regions 

 with native insectivorous birds in a similar manner 

 to that in which the United States Fish Commis- 

 sion has succeeded in re-stocking, not only our 

 inland waters, but also rivers and estuaries. Mi- 

 gratory fish, such as the shad and salmon, have 

 been dealt with in this way ; and their journeys 

 away from their breeding grounds are quite as 

 mysterious as those of birds, and perhaps less 

 understood, if that were possible. 



Instinct, habit, and the development of intelli- 

 gence have been studied, but not continuously, 



