414 



EFFECT OF TEMPERATURE UPON FACET NUMBER 



The difference in facet number per °C. is found by dividing the ob- 

 served difference between the means of two temperatures by the num- 

 ber of degrees there are between those temperatures. The per cent 

 change in the mean is found by dividing the difference in facet number 

 per °C. by the average of the two means for the observed temperatures. 



A consistent sexual difference exists in all these experiments. It is 

 impractical to combine the data for the two sexes into a single table 

 as the sex coefficient is not constant throughout. 



The results of these experiments are shown graphically in Fig. 2. 



Temperature Efect on Low Selected Bar Stock. 



The preliminary experiments on Unselected bar stock showed the 

 temperature range of the species to be practically limited to 15-30°C. 

 From this it was decided to interpolate as many intermediate experi- 



TABLE TII. 



Low Selected Bar Stock. Summary of Experiments 12, 22, and 27. Females. 



Temperature 



at which flies 



developed. 



°C. 



15 



16 



17.5 



20 



25 



27 



29 



30 



31 



Difference in 



facet No. for 



interval. 



30.80 

 30.93 

 28.39 

 24.63 

 19.12 



7.73 

 10.84 



7.71 

 Average. 



Difference in 



facet No. per 



°C. 



30.80 



20.61 



11.36 



4.93 



9.56 



3.86 



10.84 



7.71 



12.38 



Average of 

 means for 

 interval. 



173.59 

 142.73 

 113.07 

 86.56 

 64.69 

 51.26 

 41.89 

 32.70 



Percent of 



change for 



interval. 



17.74 



14.43 



10.04 



5.69 



14.73 



7.54 

 25.82 

 23.57 

 14.95 



mental temperatures as the apparatus at hand would permit. For 

 the Low Selected bar stock the temperatures were as follows: 15, 16, 

 17.5, 20, 25, 27, 29, 30, and 31°C. Summaries of these experiments 

 are included in Tables III and IV, while the results are shown graph- 

 ically in Fig. 3. From these tables it is at once apparent that temper- 

 ature has a very marked effect on the mean facet number of the Low 

 Selected bar stock. 



