462 EFFECT OF TEMPERATURE UPON FACET NUMBER 



the secondary factors in enzyme destruction, differences in viscosity, 

 or in the physical state of colloids. 



Differential temperature coefl&cients for the various separate proc- 

 esses involved in development furnish the best basis for an explana- 

 tion of the straight line feature of the curve representing the effect of 

 temperature on the rate of physiological processes. 



Facet number in the full-eyed wild stock is not affected by tem- 

 perature to a marked degree. 



The mean facet number for fifteen full-eyed females raised at 27° 

 is 859.06. 



The mean facet mmiber for the Low Selected Bar females at 27° is 

 55.13; for the Ultra-bar females at 27° it is 21.27. 



A consistent sexual difference appears in all the bar stocks, the 

 females having fewer facets. This relation may be expressed by the 

 sex coefficient, the average value of which is 0.791. 



The average observed difference in mean facet number for a dif- 

 ference of 1°C. in the en\dronment in which the flies developed is 

 3.09 for the Ultra-bar stock and 14.01 for the Low Selected stock. 



The average proportional differences in the mean for a difference 

 of 1°C. are 9.22 per cent for Ultra-bar, and 14.51 for Low Selected. 



The differences in the number of facets per °C. are greatest at the 

 low and least at the high temperatures. 



The difference in the number of facets per °C. varies with the 

 mean. 



The proportional differences in the mean per °C. are greatest at 

 the lower (15-17.5°) and higher (29-31°) temperatures and least 

 at the intermediate temperatures. 



Temperature is a factor in determining facet number only during 

 a relatively short period in larval development. 



This effective period, at 27°, comes between the end of the 3rd and 

 the end of the 4th day. 



At 15°, this period is initiated, at the end of 8 days following a 

 1st day at 27°. 



At 27° this period is approximately 18 hours long. At 15° it is 

 approximately 72 hours long. 



The number of facets and the length of the immature stage (egg- 

 larval-pupal) appear related when the whole of development is 

 passed at one temperature. 



