CROSSINGOVER IN DROSOPHILA 



155 



the greatest variations in temperature, though it was always 

 kept on top of the incubator in a south room which was kept 

 heated as evenly as possible. For this series the temperature 

 ran ordinarily from 22-24°C, but on one or two occasions reached 

 20 and 26°C. As will be seen from the results recorded, a varia- 

 tion even between these limits does not effect more than a 

 negligible change in the linkage ratios, and therefore it may be 

 disregarded. In the other two series variation was extremely 

 slight, in the incubator not more than 0.5°C, and in the ice- 

 chest 1°C. in either direction. It was found that the Pi females 

 did not lay well if placed immediately into the temperature at 

 which their eggs were to be hatched. In both the cold and the 

 heat series, therefore, the bottles were allowed to stand at room 

 temperature for twenty-four hours after the Pi pairs were intro- 

 duced before being transferred to the temperature to be tested. 

 This generally insured sufficient eggs to give the required number 

 of Fi females for the back-cross test, and had no effect on the 

 test itself. It was also found later that it made no difference 

 in what order the test series were made up. The cold test could 

 be taken first, the control second, and the heat last, or in any 

 other combination. The temperature at which the Pi females 

 laid the eggs affected the number of eggs, but only the tem- 

 peratures at which those eggs developed and hatched showed an 

 effect on the percentage of crossingover among their offspring. 

 At the control temperature flies begin to .hatch in about twelve 

 days, at 12°C. in from three to four weeks, and in the incubator 

 at 31°C. in about ten days. The first test of the effect of tem- 

 perature gave the following results : 



TABLE 5 

 b — pr — c 



Hatched at 22° 

 Hatched at 31° 

 Hatched at 13° 



per cent 



20.2 

 26.7 



27.2 



A X B 

 A X C 



X 2 = 113.5 

 X 2 = 113.5 



