188 



HAROLD H. PLOUGH 



six days. The next total, March 2 to 6, gave the control value, 

 showing that all of the eggs which had been affected by the high 

 temperature had finally been laid. 



Ineffectiveness of exposure of early larvae. A second set of 

 data gives very strong corroborative evidence In the develop- 

 ing female gonads very few oocytes are formed until the later 

 larval and pupal condition is reached. If heat affects only the 

 early oocytes, we should expect little or no increase among the off- 

 spring of females which had been exposed only in the early larval 

 condition, and conversely practically the whole increase among 

 offspring of females which had been exposed in the period from 

 the late larval to the adult stage. Cultures were exposed to 

 heat for four days after the eggs were laid, and then removed to 

 normal temperature. Similar cultures were kept at 22° for the 

 first four days and then transferred to-31.5°C. until the flies 

 hatched. The test of these females compared with their corre- 

 sponding controls follows: 



TABLE 17 



S' 



The result shows that the expectation is justified, for there is 

 practically no increase of No. 3 over No. 4, while the per cent II 

 value for No. 1 is 7 Ymits higher than No. 2 and is close to the 

 usual value shown when the females are exposed for the whole 

 period. The value given in No. 3 is more striking when com- 

 pared with the value for four days' exposure in table 15, for the 

 latter shows that such an exposure of adult flies is sufficient to 

 raise the value to the high point for an equal period. 



