HEMIPTERA. 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 individual. 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 1566, 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 astonish- 
ment among naturalists, and, in this respect, 1743 may be con- 
sidered 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 
