Essays in natural history and philosophy. Containing a series of discoveries, by the assistance of microscopes / By John Hill.

  • Hill, John, 1714?-1775.
Date:
1752
Catalogue details

Licence: Public Domain Mark

Credit: Essays in natural history and philosophy. Containing a series of discoveries, by the assistance of microscopes / By John Hill. Source: Wellcome Collection.

    31/434 (page 19)
    hires explained ; and I have found by Obfervations fince made,- that thefe Flies are produced out of Eggs of the fame Brood with the other Infedb; that the firft Appearance of both is the fame* and that it is only when the Females become fixed down on the Bark, that the Difference is feen. As foon as thofe which are to produce the mde fly are arrived at their due Growth, which is noc nearly that of the others, inftead of a Number of Eggs an Aurelia is produced, like that of other Flies, and from this the Fly foon after appears, making its Way from under the Shell, in its full Size and Proportion. It is no fooner at Liberty than it impregnates the Females all about it $ and as it has in this new State no Organ for eating, its foie Bufmefs of Life being the Propagation of the Species* it then dies* The Females after this con¬ tinue in their Places, difcharge their Eggs, and die ; and from the Brood of every Individual there are produced a great Multitude of Females and a few Males, whichare by no means to be diftinguifhed till the Period at which the Male affumes its Fly-State. The blue Worms, mentioned occafionally in this EBay, as always found among thefe Infedls, are produced from Eggs laid in the very Bodies of thefe Females, by a Fly of a very different Genus, one of the Ichneumon Kind j and after a proper Change they affume the Form of their Parents. They feed on the Juices extravafated by the Pundtures of thefe Infedts, but do them no Harm, nor is the Female hurt by foftering them in her Body. f C o E S S A Y