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 one or
of several preceding generations, are required. The son may not resemble
the father, but the grandfather, and in some instances, the likeness
re-appears only in latter generations. Agassiz states: "Alternate
generation was first observed among the Salpae. These are marine
mollusks, without shells, belonging to the family Tunicata. They are
distinguished by the curious peculiarity of being united together in
considerable numbers so as to form long chains, which float in the sea,
the mouth(_m_) however being free in each.

[Illustration: Fig. 2. ]

[Illustration: Fig. 3. ]

"Fig. 2. The individuals thus joined in floating colonies produce eggs;
but in each animal there is generally but one egg formed, which is