44? ' THE PHILOSOPHY 



gard to the manners and oeconomy of animated beings*. M. 

 Bonnet has furniihed inconteftible evidence, that feveral fpe- 

 cies of the puceron, or vine-fretter, are both oviparous and 

 viviparous. In fummer, thefe infecSts bring forth their young 

 alive ; but, in autumn, tliey depofit eggs upon the bark and 

 branches of trees. Here the intention of nature is apparent. 

 The puceron is unable to furvive the winter colds; and, there- 

 fore, though viviparous during the warm months, the fpecies 

 could not be continued without this vA{e provifion. The 

 puceron, it fliould appear, is naturally difpofed to produce live 

 young. The foetus is inclofed in a membrane, which, like 

 that of the larger animals, burfts before exclufion. But, when 

 the cold feafon commences, the general texture of the ani- 

 mals, as well as the membranes inclofing the foetus, becomes 

 more firm and tenacious j and this, perhaps is the phyfical 

 reafon why they are viviparous in fummer, and oviparous in 

 autumn. Many other flies are known to be viviparous. 

 Upon further examination, all thefe will probably be difcov- 

 ered to be alfo oviparousf . 



The puceron exhibits another phaenomenon ftill more 

 fmgular. The maxim, that multiplication prefuppofed im- 

 pregnation by fexual embraces, w^as formerly thought to be 

 univerfal. Neither fliould the reception of this maxim be 

 regarded as a matter of wonder ; for it was founded on a very 

 general and ftrong analogy. But the following fa6ts fhow, 

 that nature, though uniform in many fteps of her progrefs, is 

 not invariably limited to the fame mode of operation. On 

 the 20th day of May, M. Bonnet took a young puceron, 

 the moment after dropping from the womb of its mother, 

 and fliut it up in a glafs veflel, to prevent all poflibility of 

 communication with any individual of the fpecies. A fprig 

 of the tree on which the animal was produced, fupplied it 



* Traite d'liifecSlologle, par C- Bonnet, torn. i.p. 194. — 202. 

 f See Reaumur, torn, 8. edit. i2mo, p. 153. et leq. 



