PAIRING OF APHIDES. 239 



both male and female, and capable of producing 1 

 eggs; snails and earth-worms, however, could not 

 produce eggs, if secluded at the moment of birth as 

 the aphides were in the preceding experiments, pair- 

 ing being as indispensable with them as with the 

 distinct males and females of other animals. 



The fact discovered by M. Bonnet, which had 

 been so strangely misrepresented by Leeuwenhoeck, 

 Cestoni, and Bourguet, led him to push the in- 

 vestigation still farther, and his perseverance was 

 rewarded by the discovery of other facts still more 

 wonderful, and less to have been expected. He 

 commenced with the aphis of the elder (A. Sambuci), 

 secluding not only an individual at the moment of its 

 birth, but one of its progeny, and so on successively, 

 till he saw the fifth generation produced without any 

 intermediate pairing; and the young of the latter 

 brood, he had reason to believe, might have been 

 equally fertile, had it not been in the winter, when he 

 could not procure them a fresh elder-branch for nou- 

 rishment. In a subsequent experiment with the 

 large species which feeds on the bark of the oak 

 (Eriosoma Quercus, STEPHENS) Bonnet pushed his 

 observations as far as the ninth generation, which 

 were produced in three months, the males being 

 throughout rigorously excluded from the nurse-boxes 

 in which the females were isolated*. Lyonnet made 

 similar experiments with the aphides of the willow, 

 but without recording the number of generations 

 produced, his object being to ascertain whether they 

 ever paired at all like other insects, or whether, as 

 M. Trembley had imagined, they paired before birth. 

 Both Lyonnet and Bonnet distinctly ascertained 

 that Trembley's notion did not accord with fact, for 

 after a time the fecundity of the females becomes ex- 

 hausted, and pairing is then as indispensable to render 

 * Bonnet, (Euvres, i, 89. 



