of the Umbilical Vessels to any part of the Mother , and consequently no such Transfusion ; and that in Oviparous there is no continuity , or communication of Vessels of any kind, during the whole time of Incubation .
But these Objections carry neither the Weight nor Difficulty along with them, that they may be suppos'd to do; for in those Days there is neither Blood or Blood-Vessels, and consequently there can be no Circulation of the Blood; and the Embryo, of what Species soever, is no more than a Vegetable at that time; nor does the Fœtus of any Viviparous Creature enjoy any Circulation, or shew any signs of Animal Life, till after those Vessels, as well as others requisite to the Circulation, are compleated.
It must be confess'd, that Oviparous Animals are denied the benefit of this Communication; but that want is sufficiently compensated by a peculiar Mechanism, which directly answers the ends of Respiration , and the pressure of the Atmosphere upon the Fœtus . There is at the obtuse end of an Egg a small Cavity fill'd with Air, which is the succedaneous Instrument to the Respiratory Organs. For as soon as the Contents begin to be warm'd by the Incubation of the Hen, or any analogous Heat of Furnace or Dunghill , the several Humours of the Egg require a fermentative motion, and the Air contain'd in the Cavity or Vesicle , at the obtuse end of the Egg, is rarefied, and the Vesicle extended and enlarg'd, and consequently the other Contents are comprest; to which the fermentative motion naturally resists. But both Bodies being as well compressible as dilatable , and both having an expansive motion imprest upon them by Incubation , the Compression and Renitency will be mutual, but varied in degree, according as either, through the variation of Circumstances, shall prevail. By this means, an Alternation of Compression and Dilatation will be produc'd in both, answering the respiratory motion, by which a motion will be communicated, which, as