JOSEPH KRAFKA, JR. 437 



Efect of Temperature during the Larval Period. Initiation and Dura- 

 tion of the Effective Period at 27°. 



An examination of Table XV shows that a temperature of 27°C. for 

 1 or 2 days at the beginning of the larval period has no effect on the 

 facet number, as only three individuals out of 123 are sHghtly outside 

 the range of the stock experiments at 15°. 



Of those that passed the first 3 days at 27°, some had developed 

 beyond the point X, at which facet number is determined, since 

 their counts are characteristic of the 27° stock. Some were just 

 in the effective period when the transfer from 27 to 15° was made, 

 as shown by the fact that the counts are intermediate between those 

 characteristic of the 27 and those of the 15° stocks. Some individuals 

 were not quite so far along and hence the whole facet number-deter- 

 mining reaction was carried out at 15°. 



4 days at 27° brought nearly all individuals through the effective 

 period. Four individuals out of 104 are sHghtly above the upper 

 range of the 27° stock counts. We may conclude that the stage in 

 development, at which the facet number is being determined, is 

 passed prior to the end of 4 days at 27°. Likewise this stage is not 

 reached by the end of 2 days at 27°. 



To define this period more closely Experiment 59 was planned. 

 After many unsuccessful attempts to get a series in which the eggs 

 were not more than 1 hour apart in age, the present series was car- 

 ried through. Here the parents were allowed to lay eggs during a 

 period of 12 hours. This series includes the following number of 

 days at 27° with subsequent removal to 15°; 1 day (24 hours), 2, 

 2f , 3, 3|, 3|, 3f , and 4 days. The results are given in Table XVI 

 and in Fig. 12. 



This experiment bears out the previous one in that 1, 2, 2f, and 3 

 days at 27° did not bring the larvae up to the point X. This phase 

 of development is initiated between 3 and 3j days as shown by the 

 intermediate condition of the counts of the latter. These are pre- 

 dominated by the lower temperature. 3^ days at 27° give a pre- 

 ponderance of individuals with the 27° count. 3f days at 27° 

 have brought all but one individual through the effective period. 

 After 4 days at 27°, all individuals had completed this stage inde- 



