158 



MISCELLANEOUS PAPERS. 



Table X. — Line of generations of Sipha flava from egg to oviparous generation, 



1907. 



« Sexual generation. 



On the other hand, beginning Avith the last to be borne by the aphis 

 which had hatched March 18, and following down the series of the 

 last born of each generation, there were but 7 generations in all. 

 From this it follows that the mean number of complete generations 



Fig. 34. — Periods and succession of generations in Sipha flava, 1907. 



for the year is 11|. The first generation lasted for 93 days, from 

 March 18 to June 19, the second extended over a period of 80 days, 

 the third 84 days, and the fourth 110 days. The sixth generation 

 was the longest-lived, continuing for 158 days, the period of the 

 latest generations diminishing gradually. (See fig. 34.) As in the 

 case of Aphis maidi-radkis, if the time during which eggs are prob- 

 ably hatching in the field is taken into consideration, it will be 



