In a planet devoid of atmosphere, or a sphere glowing with its own heat, we may decide without question that life does not exist. Even in a globe in many respects like our own it would be hazardous to conjecture the kinds of organic forms in which it is manifested. Reasoning from analogy, if life exists in Mars, or other spheres in infinite space, it must have originated under much the same conditions as it originated here; at the outset the most primitive bits of protoplasm. But has life appeared in Mars? Tyndall, in graphic words, pictures the rounding of worlds from nebulous haze, and then says, "For eons, the immensity of which overwhelms man's conception, the Earth was unfit to maintain what we call life. It is now covered with visible living things. They are not formed of matter different from that around them. They are, on the contrary, bone of its bone and flesh of its flesh." Mars must come in the same category. It is a part of the original nidus from which our world was condensed, and however life originated in the past, the conditions for its origin, at least, must have been as favorable on the surface of Mars, as on the surface of the Earth, and, so far as we know to the contrary, even more favorable. In the beginning, Mars cooled and hardened with all those behaviors of contraction, condensation of vapor on its surface, erosion, etc., and it is impossible to avoid the conviction that life, as on our Earth, arose under the same physical conditions. Recalling the resemblance which Mars bears to the Earth, and the data which have already been established, we behold a world in many respects like ours, with its sunsets and sunrises, winds that sweep over its surface, the dust storms from the deserts, its snow-storms and snow-drifts, its dazzling fields of white in the north, with an occasional snow-storm that whitens the planet far down in latitude; the seasonal changes, and, most important of all, the melting ice caps, with rivulets and torrents, temporary arctic seas and frozen pools, its great expanses of vegetation and sterile plains. We have in Mars the variety of conditions under which life has assumed its infinite variety of aspects on the Earth, and which, by analogy, should have passed through similar stages in Mars. Life at the outset must have been protoplasmic; then came contractile tissue, muscular bundles, hardened structures within and without for their support, nerves to animate the muscles, and protection for nerve-trunk, either rigid or flexible. Hard parts might vary under a different force of gravity, though there might appear types of structure that could be classified with our own.