"You were right all the time, Brion," she said. "There is your alien."
Ulv joined them as they looked down at the exposed brain of the magter. The thing was so clearly evident that even Ulv noticed it.
"I have seen dead animals and my people dead with their heads open, but I have never seen anything like that before," he said.
"The invader, the alien you were looking for," Lea told him.
The magter's brain was only two-thirds of what would have been its normal size. Instead of filling the skull completely, it shared the space with a green, amorphous shape. This was ridged somewhat like a brain, but the green shape had still darker nodules and extensions. Lea took her scalpel and gently prodded the dark moist mass.
"It reminds me very much of something that I've seen before on Earth," she said. "The green-fly--_Drepanosiphum platanoides_--and an unusual organ it has, called the pseudova. Now that I have seen this growth in the magter's skull, I can think of a positive parallel. The fly _Drepanosiphum_ also had a large green organ, only it fills half of the body cavity instead of the head. Its identity puzzled biologists for years, and they had a number of complex theories to explain it. Finally someone managed to dissect and examine it. The pseudova turned out to be a living plant, a yeastlike growth that helps with the green-fly's digestion. It produces enzymes that enable the fly to digest the great amounts of sugar it gets from plant juice."
"That's not unusual," Brion said, puzzled. "Termites and human beings are a couple of other creatures whose digestion is helped by internal flora. What's the difference in the green-fly?"
"Reproduction, mainly. All the other gut-living plants have to enter the host and establish themselves as outsiders, permitted to remain as long as they are useful. The green-fly and its yeast plant have a permanent symbiotic relationship that is essential to the existence of both. The plant spores appear in many places throughout the fly's body--but they are _always_ in the germ cells. Every egg cell has some, and every egg that grows to maturity is infected with the plant spores. The continuation of the symbiosis is unbroken and guaranteed."
"Do you think those green spheres in the magter's blood cells could be the same kind of thing?" Brion asked.