AND THE LOWER ANIMALS. 131 



number of young. One of these latter was then 

 imprisoned, and it gave birth to a third generation. 

 A young specimen of this generation was placed 

 under exactly similar conditions, and gave rise to a 

 fourth, and so on. Five generations of virgin aphides 

 were produced in Bonnet' s first experiment. He after- 

 wards obtained as many as ten, in the case of the 

 spindle-tree aphis; and this nuniber has been exceeded.^ 



It seemed fair to conclude from all these experi- 

 ments, that, among aphides, a single isolated indivi- 

 dual is capable of perpetuating the species. But in 

 Zoology, of all sciences, it is especially necessary to 

 guard against hasty generalizations, and Bonnet very 

 soon proved the truth of this statement. 



About the end of the year which afforded him so 

 many interesting results, and whilst he was investi- 

 gating the aphides of the oak, Bonnet distinctly 

 observed the males and females of this species; he 

 witnessed performances exactly like those which take 

 place among other insects ; in fact, he saw the female 

 aphides produce genuine ova, instead of the virgin 

 larvae which he had before observed. This species 

 exhibited, moreover, the phenomena of solitary vivi- 

 parous reproduction which he had seen before in 

 other instances. 



* These results show with what rapidity reproduction is effected 

 among the plant-bugs. Supposing a single aphis to produce only 

 fifty young ones — which is certainly below the average — it follows 

 that one of these insects beginning to breed in spring would give 

 rise in the course of a summer to no less than 4,000,000,000,000,000 

 of larvse, which would cover a space of at least forty thousand 

 square metres. The entire surface of the globe would be covered 

 with aphides, were it not for the number and voracity of the 

 animals which prey upon them, 



K 2 



