JOSEPH KRAFKA, JR. 443 



As there may be 24 hours difference in age among the individuals 

 in a bottle, the period at 15° is practically limited to the 9th, 10th, 

 and 11th days, or the length of the period at 15° is about 72 hours. 



Comparison of the Length of the Period during Which Temperature is 



Effective on Facet Numher with the Total Length of the 



Immature Stage. 



It has been shown that the period during which temperature is 

 effective is initiated at two very remote time intervals when develop- 

 ment is carried out at 15 and 27°, respectively. Does this period 

 represent a definite stage in development? 



The total number of days required to complete development of the 

 immature stages at 15° is 31.87, while at 27° it is 9.21. This gives a 

 daily rate of 3.13 per cent total development at 15° and 10.86 per 

 cent total development at 27°. With these rates we may calculate 

 the point X. 



3 days at 27° 3 X 10.86 = 32.58 per cent 



8 " " 15° 8X 3.13 = 25.04 " " 



1 day " 27° 1 X 10.86 = 10.86 " " 



35.90 " " 



In other words, the reaction which determines the number of facets 

 that will develop in the adult is initiated at the completion of 32 to 

 36 per cent of immature development. 



Comparing now the length of the periods during which this reac- 

 tion is going on at 15 and at 27° with the total length of the imma- 

 ture stages at those temperatures, we find 18 hours at 27° and 72 

 hours at 15° as opposed to 9.21 days at 27° and 31.87 days at 15°. 

 These ratios are a fair approximation considering the experimental 

 conditions. 



Expressing the length of the effective period in percentage of the 

 total development and adding the results to those for the initiation 

 of the period, we find that the reaction which determines the num- 

 ber of facets starts at the completion of 32 per cent of development 

 and ends with the completion of 45 per cent. 



Thus the length of a particular phase of development is propor- 

 tional to that of any other phase. Reciprocally, the rate of a given 



