520 



HEMIPTERA. 



SO on almost indefinite!}', experiments having shown that the 

 power of reproduction under such circumstances may he exer- 

 cised, according to Bonnet, at least through nine generations, 

 while Duval obtained thus eleven generations in seven months, 

 his generations being curtailed at this stage not by a failure 

 of the reproductive power but b}' the approach of winter, 

 which killed his specimens ; and Kyber even observed that a 

 colony of Aphis diantJd, which had been brought into a con- 

 stantly heated room, continued to propagate for four years in 

 this manner, without the intervention of males, and even in this 

 instance it remains to be proved how much longer these phe- 

 nomena might have 

 been continued." Dr. 

 Burnett, from whom 

 we quote, considers 

 this anomalous mode 

 of increase of indi- 

 viduals as a process 

 of budding, and that 

 the whole series, like 

 the leaves of a tree, 

 constitutes but a sin- 

 gle generation, which 

 results from the union 

 of the sexes in the 

 previous fall. It has 

 always been sup- 

 posed that the final autumnal set of indi-viduals were males 

 and females alone. But Dr. Burnett states: "The terminal 

 brood has hitherto been considered, as far as I am aware, to be 

 composed exclusively of males and females, or, in other words, 

 of perfect insects of both sexes. I was surprised, therefore, on 

 examining the internal organs of the non-winged individuals, 

 to find that many of these last were not females proper, but 

 simply the ordinary gemmiparous form. Moreover so gi*eat 

 was the similarity of appearance between these two forms — 

 true females and gemmiparous individuals — that the}' could 

 be distinguished only by an examination of their internal 

 genitalia." 



517. 



