y to develope themselves wherever they may find the
requisite conditions for their existence.

"The possibility, or, rather, the high probability, that such is
the design of the oviparous generation of the _Infusoria_, and such
the common mode of the diffusion of their ova, renders the
hypothesis of equivocal generation, which has been so frequently
invoked to explain their origin in new-formed natural or artificial
infusions, quite gratuitous. If organs of generation might, at
first sight, seem superfluous in creatures propagating their kind
by gemmation and spontaneous fission, equivocal generation is
surely still less required to explain the origin of beings so
richly provided with the ordinary and recognized modes of
propagation."--pp. 31, 32.

Recent accounts show, that the dust collected from the atmosphere at
sea, many miles from land, generally contains some of these dried
animalcules and their ova. Many of these germs can be developed only in
particular localities, or under certain conditions which are rarely
fulfilled. Consequently, if there were but few of them, the species
might perish, because those few might not find their appropriate home.
But such an accident is guarded against by the vast multiplication of
these germs and their wide dispersion; for, unlike all the higher tribes
of beings except man, the same species is often found in all regions of
the globe. Very few, in comparison with the whole number, may find a
proper _nidus_; but these few then propagate with such marvellous
rapidity, as fully to replenish, if not to increase, the original stock.
Thus they have been enabled, as species, to survive even those
destroying causes which exterminated all the higher forms of animals.
Several species still exist, which were in being at the time of the
cretaceous formation, though all the other animated races belonging to
that period have perished. "These animalcules," says Ehrenberg,
"constitute a chain, which, though in the individual it be microscopic,
yet in the mass is a mighty one, connecting the organic life of distant
ages of the earth."

In view of facts like these, we may surely say, that the existence of
the infusory animalcules, and even of the entozoa, is conceivable,
supposing they could only have been produced by parents of their own
kind, and without having recourse to the anomalous and hypothetical
doctrine of equivocal generat