--far more so than we have, according to them. And I guess
that was true. They were even able to extend their life span to
something like two months.

"And to what," I inquired--but without much fire, I'm afraid; I was
losing fight--"to what am I indebted for this intrusion?"

"Necessity."

It was, to them. Their sun had begun to cool. It was their eviction
notice.

They had to move or adapt themselves to immeasurably harsher
conditions; and they had become so highly developed, so specialized,
that change of that sort would have been difficult if not impossible.
And they didn't want to change, anyway. They liked themselves as they
were.

The only other thing was to escape. They had to work for flight through
space. And they succeeded.

There were planets nearer to them than Earth. But these were enormous
worlds to them, and the conditions were intolerably harsh. They found
one planet with conditions much like those on Earth a few million years
back. It was a jungle world, dominated by giant reptiles--which were of
no use to the folk. But there were a few, small, struggling,
warm-blooded animals. Small to us, that is--they were county size to
the folk.

Some genius had a great inspiration. While the environment of the
planet itself was impossibly harsh and hostile, the conditions _inside_
these warm little animals were highly suitable!

It seemed to be the solution to their problem of survival. Small, trial
colonies were established. Communication with the space ships from home
was achieved.

The experiment was a success.

The trouble was that each colony's existence depended on the life of
the host. When the animal died, the colony died.

Life on the planet was savage. New colonies would, of course, be passed
from individual to individual and generation to generation of the host
species. But the inevitable toll of attrition from the violent deaths
of the animals appalled this gentle race. And there was nothing they
could do about it. They could give protection against disease, but they
could not control the hosts. Their scientists figured that, if they
could find a form of life having conscious power of reason, they would
be able to establish communication and a measure of control. But it was
not possible where only instinct existed.

They went ahead because they had no choice. Their only chance was to
establish their colonies, accepting the certainty of the slaughter of
hundreds upon hundreds of enti