100 LUTHER BURWAXK 



move acroft the tones with sucli ^.hf-ilul'-d rconi' 

 Urity AS to reach any given lit 1 liidst on a 



fixed day year after year. 



In Massachusetts or New York or in Ohio or 

 in Iowa, for exai )u will find the last flight 



of migratory biruv comprising the various 

 species of wood warblers and vircos, the orioles, 

 and the scarlet tanager, appearing between the 

 tenth and fifteenth of May each year, without 

 regard to the advancement of the season. 



And a few months later \'ou will note, if you 

 are obsen-ant, thai these and the other migrants 

 disappear in the fall, having taken up their re- 

 tmn voyage at about the same calendar period 

 year after year, although in one season the Sep- 

 tember days may be as hot as August and in 

 another season chill as November. 



Countless generations of heredity have fixed 

 in the mechanism of the bird's mind the instinct 

 that impels it to migrate at a fixed season; and 

 no transient or variable conditions of the imme- 

 diate environment can alter that instinct, even 

 though, in a given case, its alteration might be 

 vastly to the advantage of the individual. 



Even Unto Death 



As proving the latter point, and as further 

 illustrating the force of the instinctive time sense 



