432 EFFECT OF TEMPERATURE UPON FACET NUMBER 



ents daily, were treated to varying periods at 30° before subsequent 

 development at 15°. The upper row in the table gives the number of 

 days at 30°. Below the class distributions are given the mean facet 

 values for males and females. In the lower row is given the number 

 of days required to complete the immature stage. 



It is evident that there is no direct causal relation between the num- 

 ber of days taken to complete the immature stage and the number of 

 facets. 25, 24, and 23 days give practically the same facet counts 

 that are obtained when total development is passed at 15°. In the 

 last case 31 days are required to complete the immature stages. 

 Again, those flies hatching at 18 and 20 days are in the same facet 

 classes as those hatching in the stock experiments in 9 days at 30°. 



Why, then, is there an apparent correlation between the facet count 

 and the length of the immature period when the latter is passed 

 throughout at one temperature? We shall return to this question at 

 the end of the succeeding part of this study .^ 



The author wishes to express gratitude to Dr. Charles Zeleny, 

 under whose direction the work was done. 



Acknowledgments are also due to Doctor V. E. Shelf ord for many 

 valuable suggestions and to Doctor G. Dietrichson for the loan of 

 apparatus. 



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Simpson, S., and Rasmussen, A. T., Quart. J. Exp. Physiol, 1916, x, 159. 

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^ Krafka, J., Jr., /. Gen. Physiol, 1919-20, ii, in press. 



