for some very
rudimentary sensibility; the sponges, corals, polyps, and medusae, give
us a notion of these primitive beings. They were formed in the tepid
waters of the primary epoch. As long as there were no continents, no
islands emerging from the level of the universal ocean, there were no
beings breathing in the air. The first aquatic creatures were succeeded
by the amphibia, the reptiles. Later on were developed the mammals and
the birds.

What, again, do we not owe to the plant-world of the primary epoch, of
the secondary epoch, of the tertiary epoch, which slowly prepared the
good nutritious soil of to-day, in which the roses flourish, and the
peach and strawberry ripen?

Before it gave birth to a Helen or a Cleopatra, life manifested itself
under the roughest forms, and in the most varied conditions. A
long-period comet passing in sight of the Earth from time to time would
have seen modifications of existence in each of its transits, in
accordance with a slow evolution, corresponding to the variation of the
conditions of existence, and progressing incessantly, for if Life is the
goal of nature, Progress is the supreme law.

The history of our planet is the history of life, with all its
metamorphoses. It is the same for all the worlds, with some exceptions
of orbs arrested in their development.

The constitution of living beings is in absolute relation with the
substances of which they are composed, the environment in which they
move, temperature, light, weight, density, the length of day and night,
the seasons, etc.--in a word, with all the cosmographic elements of a
world.

If, for example, we compare between themselves two worlds such as the
Earth and Neptune, utterly different from the point of view of distance
from the Sun, we could not for an instant suppose that organic
structures could have followed a parallel development on these planets.
The average temperature must be much lower on Neptune than on the Earth,
and the same holds for intensity of light. The years and seasons there
are 165 times longer than with us, the density of matter is three times
as weak, and weight is, on the contrary, a little greater. Under
conditions so different from our own, the activities of Nature would
have to translate themselves under other forms. And doubtless the
elementary bodies would not be found there in the same proportions.
Consequently we have to conclude that organs and senses would not be the
same there a