manent and immutable, but that
they are subject to modification, and that "the existing forms of life
are descendants by true generation of pre-existing forms."[1] Most
naturalists are now inclined to admit the general truth of the theory of
evolution, but they differ widely respecting the mode in which it
occurred.

THE PROCESS OF GENERATION.

The vital _principle_, represented in the _sperm_-cell by a
spermatozooen, must be imparted to a _germ_-cell in order to effect
impregnation. After touching each other, separate them immediately, and
observe the result. If, with the aid of a powerful lens, we directly
examine the spermatozooen, it will be perceived that, for a short time,
it preserves its dimensions and retains all its material aspects. But it
does not long withstand the siege of decay, and, having fulfilled its
destiny, loses its organic characteristics, and begins to shrink.

If we examine the fertilized germ, we discover unusual activity, the
result of impregnation. Organic processes succeed one another with
wonderful regularity, as if wrought out by inexplicable intelligence.
Here begin the functions which constitute human physiology.

Generation requires that a spermatozooen be brought into actual contact
with a germ that fecundation may follow. If a spermatic cell, or
spermatozooen, together with several unimpregnated ova, no matter how
near to one another, if not actually touching, be placed on the concave
surface of a watch-crystal, and covered with another crystal, keeping
them warm, and even though the vapor of the ova envelops it, no
impregnation will occur. Place the spermatozooen in contact with an ovum,
and impregnation is instantly and perfectly accomplished. Should this
vitalizing power be termed nerve-force, electricity, heat, or motion? It
is known that these forces may be metamorphosed; for instance, nervous
force may be converted into electricity, electricity into heat, and heat
into motion, thus illustrating their affiliation and capability of
transformation. But nothing is explained respecting the real nature of
the vital principle, if we assert its identity with any of these forces;
for who can reveal the true nature of any of these, or even of matter?

ALTERNATE GENERATION.

In several insect families, the species is not wholly represented in the
adult individuals of both sexes, or in their development, but, to
complete this series, supplementary individuals, as it were, of o