162 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



The 'vitality threshold' seems to be correlated with the abrupt change in 

 developmental rate at about 20°C. Calculating the time requirement for 

 development to hatching works well by the classical day-degree accumula- 

 tion method; calculating the energy or food requirement by the calorie- 

 counter method works well only under constant temperature conditions of 

 incubation, but neither calculation works for predicting vitality. 



Acknowledgement is due for financial assistance received in support of this work 

 from the National Science Foundation. The author's sincere personal thanks are due 

 to his assistant, Marjorie Q. Kolderie for help throughout all stages of this study, 

 and to graduate student assistants John De Witt and James Baird for making some 

 determinations. My utmost appreciation is due to my colleague, Dr. A. C. Hod.son, 

 for his cooperation and for many discussions about this research. 



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