ployed by Bonnemaisoii (1951). Two lines of descent are taken from each 

 fundatrix: one line is propagated in each generation from a "first-born" 

 aphid, while the other is derived from a "last-born" individual. Males, and 

 later, oviparae finally appear almost synchronously in the two lineages despite 

 the disparity in the generation number. The time required Avaries with temper- 

 ature but is usually of the order of 50 — 60 days at 15°C. 



Since these two lineages are part of a clone, progressive nuclear differenti- 

 ations in succeeding generations could hardly be expected. This suggests that 

 the timing mechanism may be located in the cytoplasm. As the operation 

 of the "interval timer" takes no account of the number of individual or cell 

 generations which have elapsed since the fertilization of the egg, it seems 

 that the elements responsible for the timing mechanism are capable of self- 

 replication, Ике a plasmagene. Nevertheless, it is also necessary to assume 

 that these elements undergo a continuous change with time. 



Until the final critical change in the "interval timer" has supervened, all 

 eggs become female and all embryos virginoparae. It is probable that this 

 final change results in the restoration of the maternal control systems that 

 permit the egg or embryo to develop along alternative pathways in response 

 to the appropriate environmental signals. 



LITERATURE 



Bonnemaison L., 1951, Ann. Épiphyt. (С). 2: 1 — 380. 

 Lees A. D., 1959, J. Ins. Physiol., 3: 92—117. 



РЕЗЮМЕ 



Получение различных форм у тли Медоигп viciae Buckton определяется в ооцитах пли 

 в течение эмбрионального развития факторами среды, влияющими через физиологию 

 материнского организма. Определение возникновения девственниц или яйцекладущих 

 зависит от температуры и длины светового дня, определение пола зависит только от 

 температуры. Крылатость девственниц определяется прямо перед пх рождением, путем 

 влияния на мать, находящихся поблизости тлей. 



В молодых клопах, как раз полученных от основательниц, еще не бывает реакции на 

 короткий световой день. Последняя наступает лишь через некоторое время. 



307 



