TEMPERATURE COEFFICIENT OF A HETEROZYGOTE. 



Ill 



of the ommatidial counts, arranged so that each unit has the same 

 logarithmic value, corresponding to a change of 8 per cent, in 

 ommatidial number. The location of the zero point is of course 

 purely arbitrary. 



lege of scale of 



Ommatidial degrees 



means 



2.034 



1.868 



1.700 



1.533 



1.366 



+25 



+20 



+15 



+10 



+ 5 



1.199 



temperatures 15° 20° 27° 30° 



log. differences 0.336 0.345 0.279 0.371 



Fig. 3. The length of each heavy vertical line represents the difference in 

 terms of logarithms of ommatidial number between homozygous and hetero- 

 zygous ultra-bar at the respective temperatures. The numerical values are 

 given at the bottom of the figure. The heterozygotes have one full and one 

 ultra-bar factor. The logarithmic scale is represented at the left. In the next 

 column is the scale of corresponding degrees Centigrade which would produce 

 the same effect, starting with an arbitrary zero at the lowest value of the 

 present observations. It is to be noted that the difference between homozygote 

 and heterozygote on this scale is fairly constant. 



The heavy vertical lines again give the effect produced by the 

 substitution of a second ultra-bar factor for the full factor of the 

 heterozygote at the different temperatures. The second ultra-bar 

 factor at 15 C. depresses the value by an amount equal to that 

 produced by 10.3 degrees of temperature, at 20 C. by 10.2 de- 

 grees, at 27 C. by 8.4 degrees, and at 30 C. by 11.0 degrees. 

 The average depression is the same as that produced by ten de- 

 grees of increase in temperature, and considering the character of 



