410 EFFECT OF TEMPERATURE UPON FACET NUMBER 



the compound eye. Furthermore, the particular stages in develop- 

 ment at which the facet-determining reaction is initiated has been 

 ascertained by the use of the temperature differences. 



Materials and Methods. 



The bar-eyed mutant of Drosophila was first described by Tice. Considerable 

 variation was noticed in this character. Zeleny and Mattoon, and May have 

 shown that part of this variation was due to germinal differences. It was noted, 

 however, that environmental factors were responsible for the greater part of the 

 variation. 



A preliminary analysis of the temperature effects on facet number was made by 

 Seyster in this laboratory in 1916. 



The white, bar-eyed mutant of Drosophila was used. Ordinary cultural pro- 

 cedure was followed, except that the banana was sterilized by bringing it to the 

 boiling point. After cooling, the banana was inoculated with a pinch of Fleisch- 

 mann's compressed yeast. 4 and 8 ounce wide-mouth bottles were used. After 

 being fitted with one-fourth sheet of Scott Tissue Towelling and a tight cotton 

 stopper, they were subjected to 120-150°C. in a Sargent dry air electric oven. 



All matings were mass matings. Unselected stock refers to Stock 127, in which 

 Zeleny started selection in 1917. Selected Low F4 is a stock derived from Culture 

 150.3 of the fourth generation of these selections; Ultra-bar is a stock derived from 

 a 19 facet male mutant in the F2 low generation of the same selections. These 

 parent stocks were maintained at 27°C. The low facet stocks were used more 

 extensively because of the greater ease in counting, and also to eliminate as many 

 germinal differences as possible (Zeleny). 



Temperature Control. — A constant temperature of 15° was maintained in the 

 cool room. The Johnson Heat Regulation System controls the temperature by 

 forcing air over brine coils and redistributing it to the room. A constant tempera- 

 ture of 23° was maintained in a similar manner in the warm room. 



A battery of aquaria, fitted with Johnson regulators controlling the flow of hot 

 and cold water, supplied the following temperatures; — 16, 17.5, 20, 25, and 30°C. 

 27° was maintained in a Chicago Surgical and Electric Company incubator. At 

 first, very marked differences in temperature were found in various parts of this 

 incubator (1.5-3°). A 9 inch desk fan was installed in the top of the incubator, 

 with the blades inside and the motor outside. This fan was run at high speed, 

 and no further temperature differences were noticed. 



Temperature Records. — Temperature records were kept at 27° by a Tycos Re- 

 cording Thermometer. At 15 and 23°, New Tycos Thermographs were used. 

 In the aquaria, Friez Soil and Water Thermographs kept the records. 



The experimental material was kept as close to the effective elements of these 

 instruments as was possible. Checks were frequently made on the instruments 

 bv standardized thermometers. 



