est fancy had become commonplace.
According to many of our scientists, it is utterly impossible for you
to exist. Yet you say, and it must be, that there are millions upon
millions of similar beings. Think of it! Venerians, Tellurians,
Martians, the satellite dwellers of the lost space-ship, and us--so
similar mentally, yet physically how different!"

"But where does the mythology come in?" thought Nadia.

"We have unthinkably ancient legends which say that once Titan was
extremely hot, and that our remote ancestors were beings of fire, in
whose veins ran molten water instead of blood. Since our recorded
history goes back some tens of thousands of Saturnian years, and since
in that long period there has been no measurable change in us, few
of us have believed in the legends at all. They have been thought the
surviving figments of a barbarous, prehistoric worship of the sun.
However, such a condition is not in conflict with the known facts of
cosmogony, and since there actually exists such a humanity as yours--a
humanity whose bodily tissues actually _are_ composed largely of molten
water--those ancient legends must indeed have been based upon truth.

"What an evolution! Century after century of slowly decreasing
temperature--one continuous struggle to adapt the physique to a
constantly changing environment. First they must have tried to maintain
their high temperature by covering and heating their cities.--Then,
as vegetation died, they must have bred into their plants the ability
to use as sap purely chemical liquids, such as our present natural
fluids--which also may have been partly synthetic then--instead of the
molten water to which they had been accustomed. They must have modified
similarly the outer atmosphere; must have made it more reactive, to
compensate for the lowered temperature at which metabolism must take
place. As Titan grew colder and colder they probably dug their cities
deeper and ever deeper; until humanity came finally to realize that it
must itself change completely or perish utterly.

"Then we may picture them as aiding evolution in changing their body
chemistry. For thousands, and thousands of years there must have gone
on the gradual adaptation of blood stream and tissue to more and more
volatile liquids, and to lower and still lower temperatures. This must
have continued until Titan arrived at the condition which has now
obtained for ages--a condition of thermal equilibrium with space upon