dinary powers of
reproduction, and incalculable numbers, their united influence may be
said to be far more important, in all the great operations of nature,
than that of the larger and more perfectly developed organisms. They
swarm in all the seas, and play an important part in choking up harbours
and forming great deposits at the mouths of rivers. The remains of those
which have perished form great beds and strata in the crust of the
earth. The silicious stone, called Tripoli, is entirely composed of such
remains; at Bilin, in Bohemia, there is one stratum of this substance,
fourteen feet thick, one cubic inch of which is estimated to contain
forty-one thousand millions of individuals. Their extreme tenacity of
life is evinced by the fact, that many of them may be entirely
desiccated, and preserved in pure sand for several years, after which,
on the application of a drop of water, they may be restored to life. In
this dried state, M. Doyere exposed some of them to a heat equal to that
of boiling water, and afterwards revived them; though, in an active
state, if subjected to a much lower temperature, they perish. If, then,
the fully developed and mature can resist such powerful extraneous
causes of destruction, how much more must the ova possess the power of
enduring them without losing their latent life! The following extract
from Professor Owen's Lectures shows the bearing of these facts upon the
question of equivocal generation.

"The act of oviparous generation, that sending forth of countless
ova through the fatal laceration or dissolution of the parent's
body, is most commonly observed in the well-fed _Polygastria_,
which crowd together as their little ocean evaporates; and thus
each leaves, by the last act of its life, the means of perpetuating
and diffusing its species by thousands of fertile germs. When the
once thickly tenanted pool is dried up, and its bottom converted
into a layer of dust, these inconceivably minute and light ova will
be raised with the dust by the first puff of wind, diffused through
the atmosphere, and may there remain long suspended; forming,
perhaps, their share of the particles which we see flickering in
the sunbeam, ready to fall into any collection of water, beaten
down by every summer shower into the streams or pools which receive
or may be formed by such showers, and, by virtue of their tenacity
of life, read