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THE AMERICAN NATURALIST [Vol.XLVII 



of T. obscuris; 37.14 per cent, of T. molitor are dead after 3.5 

 hours at 42° as contrasted with 11.77 per cent, deaths of T. 

 obscuris. 



Exposure to cold for a long period of time causes a differential 

 mortality in the opposite direction, nearly all of T. molitor (91 

 per cent.) remaining alive while 50 per cent, of T. obscuris died. 



Subjecting a mixture of the larvae to an atmosphere of pure 

 carbon dioxide for 24 to 51 hours causes a differential mortality 

 in favor of T. molitor, only 21.33 per cent, dying after 51.5 

 hours in the carbon dioxide as contrasted with 87.18 per cent, of 

 T. obscuris. 



It has been my experience, and I understand that owners of 

 bird stores have noted the same fact, that there is a relatively 

 high death rate among the larvae of T. obscuris under natural 

 conditions, while almost none of the larvae of T. molitor die before 

 pupating. 



Ross Aiken Goktner 



The Carnegie Institution of Washington 



