looking lad of Teutonic ancestry, one of those big blond kids who fool you. He didn't look like a scientist, but his skull held more knowledge of Niobe's oceans than was good for a man. He would have to unlearn a lot of it before he took his next job, or so I thought at the time.

Anyway, Heinz came into my office looking like someone had stolen his favorite fishnet. The expression of Olympian gloom on his beak-nosed face would have done credit to Zeus. It didn't take any great amount of brains to see that Heinz was worried. It stuck out all over him. He draped himself limply in the chair beside my desk.

"We've got troubles, Chief," he announced.

I grinned at him. I knew perfectly well why he was here. Something had come up that was too big for him to handle. That was Heinz's only fault, a belief in the omnipotence of higher authority. If he couldn't handle it, it was a certainty that I could—even though I knew nothing of either his specialty or his problems. However, I liked the man. I did my best to give him the fatherly advice he occasionally needed, although he would have been better off half the time if he hadn't taken it.

"Well, what's the trouble now?" I asked. "From the look on your face it must be unpleasant. Or maybe you're just suffering from indigestion."

"It's not indigestion, Chief."

"Well, don't keep me in suspense. Tell me so I can worry too."

I didn't like the way he looked. Of course, I'd been expecting trouble for the past year. Things had been going far too smoothly.

"Oysters!" Bergdorf said laconically.

"Oysters?"

I looked at him incredulously. Bergdorf sat straight up in his chair and faced me. There was no humor in his eyes. "For God's sake! You frightened me for a moment. You're joking, I hope."

"Far from it," Bergdorf replied. "I said oysters and I mean oysters. It's no joke! Just who was the unutterable idiot who planted them here?"

It took a minute before I remembered. "Hartmann," I said. "Of the BIT. He ordered them delivered at the request of Kron Avar and Tovan Harl. I suppose Harl planted them. I never paid very much attention to it."

"You should have. It would have been better if they had imported Bengal tigers! How long ago did this infernal insanity happen?"

"Right after the Agreement was signed, I guess. I'm sure it was no earlier than that, because Niobians met up with oysters for the first time at that affair." I still didn't get it, but there was no doubt that Heinz was serious. I tried to remember something about oysters, but other than the fact that they were good to eat and produced pearls I could think of nothing. Yet Bergdorf looked like the end of the world was at hand. There was something here that didn't add up. "Well, get on with it," I said. "As far as marine biology is concerned I'm as innocent as a Lyranian virgin. Tell me—what's wrong with the oysters?"

"Nothing! That's the trouble. They're nice healthy specimens of terrestrial Ostrea lurida. We found a floating limb with about a dozen spat clinging to it."

"Spat?"

"Immature oysters."

"Oh. Is that bad?"

"Sure it's bad. I suppose I'd better explain," Bergdorf said. "On Earth an oyster wouldn't be anything to worry about, even though it produces somewhere between sixteen and sixty million fertile eggs every year. On Earth this tremendous fertility is necessary for survival, but here on Niobe where there are no natural enemies to speak of, it's absolutely deadly!

"Just take these dozen spat we found. Year after next, they'd be breeding size, and would produce about three hundred million larvae. If everything went right, some three years later those three hundred million would produce nine thousand trillion baby oysters! Can you image how much territory nine thousand trillion oysters would cover?"

I stopped listening right then, and started looking at the map of Niobe pinned on the wall. "Good Lord! They'd cover the whole eastern seaboard of Alpha from pole to pole."

Bergdorf said smugly, "Actually, you're a bit over on your guess. Considering the short free swimming stage of the larvae, the slow eastern seaboard currents, poor bottom conditions and overcrowding, I doubt if they would cover more than a thousand miles of coastline by the fourth year. Most of them would die from environmental pressures.

"But that isn't the real trouble. Niobe's oceans aren't like Earth's. They're shallow. It's a rare spot that's over forty fathoms deep. As a result, oysters can grow almost anywhere. And that's what'll happen if they aren't stopped. Inside of two decades they'll destroy this world!"

"You're being an alarmist," I said.

"Not so much as you might think. I don't suppose that the oysters will invade dry land and chase the natives from one rain puddle to another, but they'll grow without check, build oyster reefs that'll menace navigation, change the chemical composition of Niobe's oceans, pollute the water with organic debris of their rotting bodies, and so change the ecological environment of this world that only the hardiest and most adaptable life forms will be able to survive this!"

"But they'll be self-limiting," I protested.

"Sure. But by the time they limit themselves, they will eliminate about everything else."

"If you're right, then, there's only one thing to do. We'll have to let the natives know what the score is and start taking steps to get rid of them."

"Oh, I'm right. I don't think you'll find anyone who'll disagree with me. We kicked this around at the Lab for quite a spell before I came up here with it."

"Then you've undoubtedly thought of some way to get rid of them."

"Of course. That was one of the first things we did. The answer's obvious."

"Not to me."

"Sure. Starfish. They'll swamp up the extra oysters in jig time."

"But won't the starfish get too numerous?"

"No. They die off pretty fast without a source of food supply. From what we can find out about Niobe's oceans, there is virtually no acceptable food for starfish other than oysters and some microscopic animal life that wouldn't sustain an adult."

"Okay, I believe you. But you still leave me cold. I can't remember anything about a starfish that would help him break an oyster shell."

Bergdorf grinned. "I see you need a course in marine biology. Here's a thumbnail sketch. First, let's take the oyster. He has a big muscle called an adductor that closes his shell. For a while he can exert a terrific pull, but a steady tension of about nine hundred grams tires him out after an hour or so. Then the muscle relaxes and the shell gapes open. Now the starfish can exert about thirteen hundred grams of tension with his sucker-like tube feet, and since he has so many of them he doesn't have to use them all at one time. So, by shifting feet as they get tired, he can exert this pull indefinitely.

"The starfish climbs up on the oyster shell, attaches a few dozen tube feet to the outside of each valve and starts to pull. After a while the oyster gets tired, the shell opens up, and the starfish pushes its stomach out through its mouth opening, wraps the stomach around the soft parts of the oyster and digests it right in the shell!"

I shuddered.

"Gruesome, isn't it?" Bergdorf asked happily. "But it's nothing to worry about. Starfish have been eating oysters on the half shell for millions of years. In fact I'll bet that a starfish eats more oysters in its lifetime than does the most confirmed oyster-addict."

"It's not the fact that they eat them," I said feebly. "It's the way they do it. It makes me ill!"

"Why should it? After all a starfish and a human being have a lot in common. Like them, you have eaten oysters on the half shell, and they're usually alive when you gulp them down. I can't see where our digestive juices are any easier on the oyster than those of a starfish."

"Remind me never to eat another raw oyster," I said. "On second thought you won't have to. You've ruined my