JOSEPH KRAFKA, JR. 



411 



The temperature of the banana in which the larvae were developing was tested 

 by inserting a thermometer through the cotton plug into the food. Only very 

 slight differences were found between the food and the surrounding medium. 



The temperatures as given in the experimental data vary at most ±0.5°C. 



At the high temperatures, 29 and 31°, additional checks were made oh the rate 

 of metamorphosis and facet number by using a water thermostat. This instru- 

 ment is of the type used by physical chemists. It is a battery jar suppUed with a 

 U-tube mercury regulator closing a secondary heating system by relay. A 3- 

 inch, motor-driven fan keeps the water agitated. Variations in temperature do 

 not exceed =t0.05°C. 



Fig. 1. Camera lucida drawings of the heads of two Ultra-bar females. The 

 one on the left has 21 facets; reared at 27°. The one on the right has 48 facets, 

 reared at 15°. The magnification is the same in both drawings. X 100. 



Technique. — Counts of the facets were made by the methods described by May. 

 The flies were etherized and placed one at a time on a wooden counting block. 

 The upper surface of this block was cut to a slight incline in order to bring the com- 

 pound eye into the best position for focusing. The facets were counted under a No. 

 4 ocular and a No. 3 Leitz objective with direct illumination from a 60 watt 

 tungsten lamp. Adjustments were made with the fine thumb-screw to accommo- 

 date the curvature of the head. Facets were recorded immediately after each 

 individual count. The material was then preserved in alcohol. 



