294 CHARLES ZELENY 



mutation of full eye; it is in the same direction as the selection 

 which was being carried on in the material, and, lastly, it has a 

 greatly increased dominance, so that it is dominant not only over 

 full eye, but also over bar eye. 



TEMPERATURE CONTROL 



Eye-facet number in Drosophila has exceptional advantages in 

 a quantitative study of both germinal and environmental factors. 

 The earlier studies of the germinal factors affecting this character 

 by Zeleny and Mattoon ('15) and H. G. May ('17) were made 

 difficult and unsatisfactory in many ways because of the disturb- 

 ing presence of uncontrolled environmental factors, and it was 

 realized that the latter must be eliminated in considerable de- 

 gree before further progress could be made with the former. 

 Experiments in this laboratory by Seyster ('19) and Krafka 

 ('20) have shown that temperature is the most important 

 of these factors. It affects facet number in a marked and def- 

 inite manner. Adequate facilities for temperature control in the 

 Vivarium Building have made possible the analysis of the germ- 

 inal factors preexisting in the bar stocks and also the isolation 

 of new factors as they arise. 



All of the facet numbers recorded in the present paper were 

 from individuals raised at 27° ± 0.5°. The incubator used was 

 no. 2, made by the Chicago Surgical and Electrical Company. 

 The heat unit is a high-resistance wire coil and contact is accom- 

 plished by the bending of a diaphragm. The platinum contact 

 points must be kept clean. A test of the incubator as purchased 

 showed that there was a difference of three or more degrees in 

 the different parts of the chamber. A 12-inch General Electric 

 desk fan with lengthened shaft so that it could be installed with 

 the motor outside and the blades inside of the chamber has acted 

 in a satisfactory manner in keeping the air stirred. Frequent 

 checks were made of the temperature of the banana food in which 

 the larvae were developing, which showed that under these con- 

 ditions the food temperature differed from the air temperature 

 by two-tenths of a degree at most. A Tycos, ribbon type, bi- 

 record thermometer made by the Taylor Instrument Company 



