168 ELMER ROBERTS 



for the males and 19.13 ± 0.052 for the females. There can be 

 no doubt, then, that 'crossing-in' has modified the character. 



c. Effect of temperature . In this series, as in the other, high 

 temperature increased the size of the wing, and the increase was 

 greater among the males than among the females. To determine 

 more exactly the effect of temperature, the following experiment 

 was performed. After the parents were selected for the F29 

 generation of 'crossed-in-and-selected' series C, they were 

 allowed to deposit eggs in four bottles, two of which were put 

 into an incubator set to run from 27°C. to 28°C. The tem- 

 perature, however, ranged from 26.7°C. to 35.7°C. This high 

 temperature was caused by the extremely warm weather in the 

 summer of 1916. The other two bottles were kept at the lab- 

 oratory temperature, which ranged from 18°C. to 35.1°C., but 

 for the most part around 22°C. to 24°C. Readings were made 

 twice daily, morning and evening. The average temperature in 

 the incubator during the experiment was 28.4°C. and in the lab- 

 oratory 25.9°C. Table 7 gives the means, standard deviations, 

 and coefficients of variability of males and females separately. 

 Table 9 gives the means of the generations by combining the 

 males and females. 



From text figure 2 a comparison can be made between the 

 generations produced in the incubator and those kept in the 

 laboratory. The difference is very marked even though the 

 temperature in the laboratory approached that in the incubator, 

 due to the hot summer weather. The average of the means of 

 the males and females in the laboratory is 24.49 ± 0.14 and of 

 those in the incubator 42.79 =t 0.25. These aver.iges are for 

 F29 to F33 generations in both the laboratory and incubator series. 

 It must be clear, then, that temperature has a marked effect 

 upon the somatic expression of vestigial wings. 



It is to be noted that in the incubator series the F29 generation 

 has a much lower mean than any of the other generations. The 

 two bottles were not placed in the incubator until after all the 

 eggs had been deposited and many pupae formed. This seems to 

 indicate that the effect of high temperature took place between 

 the fertilization of the egg and the pupal stage. 



