420 



EFFECT OF TEMPERATURE UPON FACET NUMBER 



The Temperature Coefficient. 



(a) Changes in Mean Facet Number Accompanying a Unit Tempera- 

 ture Change. — In the fifth rows of Tables I to VI are given the average 

 differences in facet number per °C. for the temperature intervals in- 

 dicated. These temperature differences are shown in Fig. 6. 



The greatest change in facet number for a change in temperature of 

 1° is that for the interval 15-16° in the Low Selected males. Here 1° 

 produces a difference of 32.66 facets in the mean values. 



Facet 

 numlDer 



30 

 20 



10 



15^ 



20' 



25* 



30' 



Tennpereiture 



Fig. 6. Number of facets difference in the mean accompanying a difference of 

 1° in temperature in the environment in which the flies were raised. The solid 

 line represents the Unselected bar stock, the broken line the Low Selected, and 

 the dot and dash line the Ultra-bar. The upper curve of a pair is for the males in 

 each case. 



The least change for a difference of 1° in temperature is for the in- 

 terval 29-31° in the Ultra-bar females. Here a difference of 1° in 

 temperature produces only 1.33 facets difference between the two 

 means. 



Obviously a difference of 1° does not produce a constant difference 

 in the mean number of facets. The greater differences are produced 

 at the lower temperatures, the lesser at the higher. Again, the greater 



