418 



EFFECT OF TEMPERATURE UPON FACET NUMBER 



The labor involved in the preparation and in the counting renders 

 the full-eyed stock unsuitable for a more elaborate study. 



The counts at hand show that temperature does not affect facet 

 number in full-eye to any appreciable extent. One female of the two 

 at 15° was sKghtly outside the range of the counts at 27°. The three 

 flies mounted and counted were taken at random from a hatch at 

 15°. The remainder of the hatch was examined under the binocular. 

 No differences were detected between these flies and the three counted 



TABLE VII. 



Effect of Temperature upon Facet Number in the Full-Eyed Stock. 



Temperature Effects on the Three Bar Stocks Compared. 



For a direct comparison, the mean facet numbers of the females of 

 the three stocks are shown in Fig. 5. Here they are all plotted to the 

 same scale. The lower curve is that of the Ultra-bar stock, the middle 

 one is that of the Low Selected bar stock, while the upper one is that of 

 the Unselected bar stock. 



In the Ultra-bar stock, the mean for the females is reduced from 

 51.51 facets at 15° to 21.27 at 27°. In the Low Selected, the mean is 

 reduced from 189.00 facets at 15° to 55.13 at 27°. In the Unselected 

 bar stock, the mean is 213.67 at 15° and 81.08 at 25°. There is a very 

 marked reduction in facet number with increase in temperature in 

 each of these three stocks. 



