Though the Earth and Mars agree in being planets, they differ constitutionally in several important respects. Even to us the curious network that enshrouds the Martian disk suggests handicraft; it implies it much more when considered from a Martian standpoint. CHAPTER XXXI THE HUSBANDING OF WATER That the canals and oases are of artificial origin is thus suggested by their very look; when we come to go further and inquire into what may be their office in the planet’s economy, we find that the idea in addition to its general probability now acquires particular support. For this we are indebted in part to study of their static aspect, but chiefly to what has been learnt of their kinematic action. Dearth of water is the key to their character. Water is very scarce on the planet. We know this by the absence of any bodies of it of any size upon the surface. So far as we can see the only available water is what comes from the semi-annual melting at one or the other cap of the snow accumulated there during the previous winter. Beyond this there is none except for what may be present in the air. Now, water is absolutely essential to all forms of life; no organisms can exist without it. But as a planet ages, it loses its oceans as has before been explained, and gradually its whole water supply. Life upon its surface is confronted by a growing scarcity of this essential to existence. For its fauna to survive it must utilize all it can get. To this end it would be obliged to put forth its chief endeavors, and the outcome of such work would result in a deformation of the disk indicative of its presence. Lines of communication for water purposes, between the polar caps, on the one hand, and the centres of population, on the other, would be the artificial markings we should expect to perceive.