280 



THE AMERICAN NATURALIST 



[Vol. LVI 



times. No great importance is probably to be attached 

 to these ditferences between the several groups, however, 

 though some of them appear significant statistically. 



Conclusion 



From the experiments herein described, involving the 

 determination of the total duration of life in 4,330 indi- 

 vidual flies, it may be safely concluded that no sensible 

 error will be introduced into duration of life experiments 

 on Drosophila as a result of completely anesthetizing the 

 flies with ether, at least up to as many as four times in 

 the course of their lives. 



LITEEATUEE CITED 



32. Pearl, E. and Parker, S. L. Experimental Studies on the Duration 



of Life II. Heredatary Differences in Duration of Life of Line- 

 174-187, 1922. ^ ' ' PP 



33. Morgan, T. H. The Failure of Ether to Produce Mutations in Dro- 



sophila. American Naturalist, Vol. 48, pp. 705-711, 1914. 



34. Pearl, E. and Kelly, F. C. Forecasting the Growth of Nations. The 



Future Population of the World and its Problems. Harper's Mag., 

 Vol. 142, pp. 704-713, 1921. 



