he mud of the Nile, and struggling to disentangle their hinder
parts. It was not considered, that animals and vegetables have been
perpetually improving by reproduction; and that spontaneous vitality was
only to be looked for in the simplest organic beings, as in the smallest
microscopic animalcules; which perpetually, perhaps hourly, enlarge
themselves by reproduction, like the roots of tulips from seed, or the
buds of seedling trees, which die annually, leaving others by solitary
reproduction rather more perfect than themselves for many successive
years, till at length they acquire sexual organs or flowers.

A third prejudice against the existence of spontaneous vital
productions has been the supposed want of analogy; this has also
arisen from the expectation, that the larger or more complicated
animals should be thus produced; which have acquired their present
perfection by successive generations during an uncounted series of
ages. Add to this, that the want of analogy opposes the credibility of
all new discoveries, as of the magnetic needle, and coated electric
jar, and Galvanic pile; which should therefore certainly be well
weighed and nicely investigated before distinct credence is given
them; but then the want of analogy must at length yield to repeated
ocular demonstration.

_Preliminary observations._

II. Concerning the spontaneous production of the smallest microscopic
animals it should be first observed, that the power of reproduction
distinguishes organic being, whether vegetable or animal, from
inanimate nature. The circulation of fluids in vessels may exist in
hydraulic machines, but the power of reproduction belongs alone to
life. This reproduction of plants and of animals is of two kinds,
which may be termed solitary and sexual. The former of these, as in
the reproduction of the buds of trees, and of the bulbs of tulips, and
of the polypus, and aphis, appears to be the first or most simple mode
of generation, as many of these organic beings afterwards acquire
sexual organs, as the flowers of seedling trees, and of seedling
tulips, and the autumnal progeny of the aphis. See Phytologia.

Secondly, it should be observed, that by reproduction organic beings
are gradually enlarged and improved; which may perhaps more rapidly
and uniformly occur in the simplest modes of animated being; but
occasionally also in the more complicated and perfect kinds. Thus the
buds of a seedling tree, or the bulbs of seed