-GENERATION OF INSECTS. 19 



shoots of which have swarmed with aphides all the 

 winter, and the leaves below are covered with honey- 

 dew. We tried the experiment of wiping it off from 

 a leaf, but no more was formed when it was protected 

 by a piece of writing-paper from the aphides above; 

 while the writing-paper became sprinkled all over 

 with it in a few hours. By means of a lens, also, we 

 have actually seen the aphides ejecting the honey - 



The almost instantaneous appearance of these des- 

 tructive insects in great numbers at the same time, is 

 taken notice of with wonder by almost every writer. 

 This circumstance, it must be confessed, gives con- 

 siderable plausibility to the notion of their being 

 brought by winds, for whence, we may be asked, 

 -could they otherwise come ? Simply, we reply, from 

 the eggs deposited the preceding autumn, which, hav- 

 ing all been laid at the same time, and exposed to the 

 same degrees of temperature, are of course all simul- 

 taneously hatched. In the case of the aphides, also, 

 the fecundity is almost incalculable. Reaumur pro- 

 ved by experiment, that one aphis may be the pro- 

 genitor of 5,904,900,0^0 descendants during its life; 

 and Latreille says, a female during the summer 

 months usually produces about twenty-five a day. 

 Reaumur further supposes, that in one year there 

 imy be twenty generations. We ourselves have 

 counted more than a thousand aphides on a single leaf 

 of the hop; and in seasons when they are abundant 

 when every hop-leaf is peopled with a similar swarm 

 the number of eggs laid in autumn must be, to use 

 the words of Good, ' myriads of myriads.' The pres- 

 ervation and hatching of these eggs in the ensuing 

 spring must, it is obvious, depend on the weather and 



* J. R. 



