The philosophy of natural history / by William Smellie.

  • William Smellie
Date:
1808
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Licence: Public Domain Mark

Credit: The philosophy of natural history / by William Smellie. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    gar J to the manners and oeconomy of animated beings*. M. Bonnet has furnilhed inconteftible evidence, that feveral fpe- cics of the puceron, or vine-fretter, are both oviparous and viviparous. In fummcr, thefe infects bring forth their young alive but, in autumn, they 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 wife provifion. The puceron, it fhould 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 •, 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 oviparous-]-. The puceron exhibits another phaenomenon ftill more Angular. The maxim, that multiplication prefuppofed im- pregnation by fexual embraces, was formerly thought to be univerfal. Neither fhould 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 facts 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 fhut it up in a glafs veffel, to prevent all poffibility of communication with any individual of the fpecies. A fprig of the tree on which the animal was produced, fupplied it • Traite d'lnfe&ologie, par C. Bonnet, torn. t.p. 194.—202.