| | | | | | | |
--C--C--C-- to O--Si--O--Si--O--Si,
| | | | | | | |

with organic radicals on the side links. These organisms were a
transitional type, with silicone tissues and water body fluids,
resembling the earthly amphibians, and are now practically extinct.
There are a few species, something like segmented worms, still to be
seen in the backwaters of the central seas.

A further development occurred when the silicone chain animals began
to get short-chain silicones into their circulatory systems, held in
solution by OH or NH_{2} groups on the ends and branches of the
chains. The proportion of these compounds gradually increased until
the water was a minor and then a missing constituent. The larger
mobile species were, then, practically anhydrous. Their blood consists
of short-chain silicones, with quartz reinforcing for the soft parts
and their armor, teeth, etc., of pure amorphous quartz (opal). Most of
these parts are of the milky variety, variously tinted with metallic
impurities, as are the varieties of sapphires.

These pure silicone animals, due to their practical indestructibility,
annihilated all but the smaller of the carbon animals, and drove the
compromise types into odd corners as relics. They developed into a
fish-like animal with a very large swim-bladder to compensate for the
rather higher density of the silicone tissues, and from these fish the
land animals developed. Due to their high density and resulting high
weight, they tend to be low on the ground, rather reptilian in look.
Three pairs of legs are usual in order to distribute the heavy load.
There is no sharp dividing line between the quartz armor and the
silicone tissue. One merges into the other.

The dominant pure silicone animals only could become mobile and
venture far from the temperate equatorial regions of Uller, since they
neither froze nor stiffened with cold, nor became incapacitated by
heat. Note that all animal life is cold-blooded, with a negligible
difference between body and ambient temperatures. Since the animals
are silicones, they don't get sluggish like cold snakes.

5. PLANT LIFE

The plants are of the carbon-metabolism, silicate-shell type, like the
primitive animals. They spread out from the equator as far as they
could go before the baking polar summers killed them. They have normal
seasonal growth in the temperate zones and remain dormant and frozen
in the winter. At th