HEMIPTEEA. 125 



After having stated the extraordinary facts, which he relates 

 with the most perfect simplicity, Charles Bonnet, examining at 

 the end of the fine season specimens of the winged oak-tree aphis, 

 was able to be present at their nuptials. He preserved the females 

 with great care, and saw, not without profound astonishment, that 

 they gave birth, not to small living insects, as was the case in the 

 first experiments, but to eggs of a reddish colour, which were 

 stuck fast to each other, on the stem or stalk of the plant. 



A short time afterwards, this illustrious observer was able to 

 convince himself that the oak-tree plant-lice, whose nuptials he 

 had witnessed in the autumn, present the same phenomena of 

 solitary and viviparous propagation, already so often mentioned 

 by him. 



At last some new observations permitted him to establish beyond 

 all doubt the connection of these facts, in appearance so contra- 

 dictory. He discovered that, during the whole of the fine season, 

 the plant-lice are solitary and viviparous, but that towards the 

 autumn these creatures return to the ordinary course of things, 

 and are propagated by eggs, whose development requires the co- 

 operation of a male and female individval. These eggs are hatched 

 in spring, and produce only viviparous plant-lice. In the autumn 

 the males and females show themselves, and from that moment 

 ovipositing recommences. These curious facts, seen and published 

 more than a century ago, have been verified many times since. 



In 1866, M. Balbiani asserted that the plant-lice are herma- 

 phrodite, or of both sexes at the same time, which would explain 

 the facts observed by Charles Bonnet. But the anatomical proofs 

 appealed to by Balbiani in support of this idea are far from esta- 

 blishing the existence of this arrangement of sexes among them. 

 The observations of Charles Bonnet produced profound astonishment 

 among naturalists, and, in this respect, 1743 may be considered as 

 a memorable year. 



The simple statement of the few experiments which he made, 

 and which we have cited, has sufficed to show how rapid is the 

 multiplication of aphides. A single female produced generally 90 

 young ones ; at the second generation these 90 produce 8,100 ; these 

 give a third generation, which amounts to 729,000 insects ; these, 

 in their turn, become 65,610,000 ; the fifth generation, consisting 



