tes, platelets ... leucocytes ... everything seems normal."
Her voice was dull, exhausted, her eyes blinking with fatigue as
she stared into the tube.

Anger at defeat burned through Brion. Even faced with failure, he
refused to accept it. He reached over her shoulder and savagely
twisted the turret of microscope until the longest lens was in
position. "If you can't see anything--try the high power! It's
there--I know it's there! I'll get you a tissue specimen."
He turned back to the disemboweled cadaver.

His back was turned and he did not see that sudden stiffening of her
shoulders, or the sudden eagerness that seized her fingers as they
adjusted the focus. But he did feel the wave of emotion that welled
from her, impinging directly on his empathetic sense. "What is it?"
he called to her, as if she had spoken aloud.

"Something ... something here," she said, "in this leucocyte. It's
not normal structure, but it's familiar. I've seen something like it
before, but I just can't remember." She turned away from the
microscope and unthinkingly pressed her gory knuckles to her
forehead. "I know I've seen it before."

Brion squinted into the deserted microscope and made out a dim shape
in the center of the field. It stood out sharply when he
focused--the white, jellyfish shape of a single-celled leucocyte. To
his untrained eye there was nothing unusual about it. He couldn't
know what was strange, when he had no idea of what was normal.

"Do you see those spherical green shapes grouped together?" Lea
asked. Before Brion could answer she gasped, "I remember now!" Her
fatigue was forgotten in her excitement. "_Icerya purchasi_, that
was the name, something like that. It's a coccid, a little scale
insect. It had those same shapes collected together within its
individual cells."

"What do they mean? What is the connection with Dis?"

"I don't know," she said; "it's just that they look so similar. And
I never saw anything like this in a human cell before. In the
coccids, the green particles grow into a kind of yeast that lives
within the insect. Not a parasite, but a real symbiote...."

Her eyes opened wide as she caught the significance of her own
words. A symbiote--and Dis was the world where symbiosis and
parasitism had become more advanced and complex than on any other
planet. Lea's thoughts spun around this fact and chewed at the
fringes of the logic. Brion could sense her concentration and
absorption. He did nothin