generations, and of fifty at an average in each
generation; so that the sum of fifty multiplied by fifty, and
that product again multiplied by fifty nine times, would give
the product of one egg only in countless millions; to which
must be added the innumerable eggs laid by the tenth
generation for the renovation of their progeny in the ensuing
spring.]

[Footnote: _The honey'd sap_, l. 352. The aphis punctures
with its fine proboscis the sap-vessels of vegetables without
any visible wound, and thus drinks the sap-juice, or
vegetable chyle, as it ascends. Hence on the twigs of trees
they stand with their heads downwards, as I have observed, to
acquire this ascending sap-juice with greater facility. The
honey-dew on the upper surface of leaves is evacuated by
these insects, as they hang on the underside of the leaves
above; when they take too much of this saccharine juice
during the vernal or midsummer sap-flow of most vegetables;
the black powder on leaves is also their excrement at other
times. The vegetable world seems to have escaped total
destruction from this insect by the number of flies, which in
their larva state prey upon them; and by the ichneumon fly,
which deposits its eggs in them. Some vegetables put forth
stiff bristles with points round their young shoots, as the
moss-rose, apparently to prevent the depredation of these
insects, so injurious to them by robbing them of their chyle
or nourishment.]

[Footnote: _The tadpole swims_, l. 359. The progress of a
tadpole from a fish to a quadruped by his gradually putting
forth his limbs, and at length leaving the water, and
breathing the dry air, is a subject of great curiosity, as it
resembles so much the incipient state of all other
quadrupeds, and men, who are aquatic animals in the uterus,
and become aerial ones at their birth.]

"So human progenies, if unrestrain'd,
By climate friended, and by food sustain'd, 370
O'er seas and soils, prolific hordes! would spread
Erelong, and deluge their terraqueous bed;
But war, and pestilence, disease, and dearth,
Sweep the superfluous myriads from the earth.
Thus while new forms reviving tribes