_Courtesy of the U. S. Bureau of Fisheries._]

Beyond the laboratory building was the wharf to which the two steam yachts attached respectively to the station and the M. B. L. were tied up. Beyond that again was a second pier, that of the Revenue Cutter service, where lay, with banked fires, one of the guardians of American seas, a man ever on duty at the wireless receiver. Beyond the pier the land curved to the point opposite the Elizabeth Islands, while in the narrow strait or 'hole' between, the tide for all Buzzards Bay surged out or in as the ebb and flow compelled.

As captain of the fish-trap crew and active in collection, Colin had the run of both laboratories and the day always seemed too short for him.

Every investigator's work was a matter of personal interest to him and he talked 'research' all the day long, though too tired to dream of it at night. Nor did he forget his swimming, and at the beach in Buzzards Bay he swam a mile or so each day, the admiration and the envy of all the M. B. L. students. But Colin speedily won their friendship, for he never hesitated to help other swimmers in every way he could, even teaching little tricks of style that were all his own and which had gone far to win him his championship.

As Director Prelatt had promised, Colin was given an opportunity to keep some research work in hand, although he found--as had been foretold--that he had but little time for it. The director was engaged upon a most interesting and important investigation, which, like all those that were in progress at the laboratory, had a strong economic value. This was the study of the life history of the whelk.

"At first sight," the director said to him, when explaining the problem, "it does not seem as though the biology of a sea-snail were a matter of much importance to the country, but as a matter of fact, to a great extent the oyster industry--which reaches millions of dollars annually and gives employment as well as food to thousands of people--depends upon that very thing."

"Just how, Mr. Prelatt?" inquired Colin.

"All creatures have their own special enemies," the director answered; "and everything is so equally balanced that there are enough oysters born to keep up the supply in spite of the attacks of the whelk, or oyster-drill as it is termed. When man comes on the scene, however, and commences to dredge the oysters, the combination of the market and the drill together is too much for the oyster-beds and they soon become depleted."

"That's the way it is with fish, too!"

"With everything," was the a.s.senting answer. "Now there are two ways to overcome this condition. One is the way in which we handle the same question with fish--by artificially hatching millions more eggs every year than would have been hatched during a state of nature. The other is by attacking the enemy of the oyster and thus enlarging the chances of those that hatch naturally. The latter we can't do with fish."

"Why not, sir?"

"Because the enemies of fish are numerous and free-swimming," was the answer, "and also because fish produce an enormous amount of eggs.

Oysters do also, but fertilization is so largely a matter of chance that but a few of the tens of thousands of eggs ever really have a chance to become young oysters. You can help that in two ways, one by preparing the ground so that everything is made easy for the young oysters to have a chance, the other by thinning them out or transplanting the young oysters or 'spat' as they are called, improving and enlarging the beds."

"That ought to help settle it, I should think."

"It is not enough. Enemies also must be kept at bay."

"I should think the oyster, in its tough sh.e.l.l, would be practically free from enemies," remarked Colin.

"On the contrary, it has a large number. A great many kinds of fish, such as skates, for example, will eat oysters, and many owners of oyster-beds have surrounded their holdings with an actual stockade of stakes."

"Like the pioneers had against the Indians?"

"Just the same," a.s.sented the director. "Drum-fish are hostile on the Atlantic coast, and on the Pacific a very substantial stockade is required against the invasion of sting-rays. More destructive still are the starfish."

Colin stared at the director in surprise.

"Starfish!" he said, "those little starfish? Why, they're soft and they haven't any teeth or anything to crush an oyster sh.e.l.l with."

"They're small and they're soft and they haven't any teeth at all," said the director, "but starfish cost the oyster industry at least five million dollars a year."

"But how?" queried Colin; "I don't see how they can work it."

"What is a starfish?"

The boy thought for a moment.

"It's an echinoderm," he said, "generally with five arms, that lives only in the sea, has a simple stomach, and feeds on the minute organisms in the water."

"There you're wrong," said the director. "It lives only in the sea, that's right enough, but you haven't proper regard for a starfish's powers of digestion. It feeds on mussels, oysters and other sh.e.l.lfish.

Can it swim?"

"I don't think so, sir," said Colin, after a moment's thought, "it crawls."

"How?"

"I don't know, Mr. Prelatt."

"By thousands of sucker-like feet on the under side of it," he was told.

"So you see it can crawl to and over an oyster-bed."

"But even so, wouldn't an oyster shut tight at the approach of danger?"

suggested Colin.

"That doesn't make any difference to the starfish," was the reply, "he'll open the oyster."

"How, sir?"

"What keeps an oyster closed?"

"The muscle, sir, because when it is dead it flies open."

"Very good. Do muscles grow tired?"

"Mine do," said Colin, smiling, "and I suppose the muscles of oysters are the same way."

"Exactly. Now what happens is this. The starfish crawls along until he finds an oyster which he thinks will suit his taste. As he crawls near or on it, the oyster closes up tight. The starfish--taking plenty of time--fastens himself to the sh.e.l.l, having two of his 'arms' on one sh.e.l.l and the suckers of the other three 'arms' attached to the other sh.e.l.l. Then the starfish starts to pull."

"But isn't the oyster stronger?"

"Much stronger," agreed the director, "but the starfish doesn't know enough to quit. The pull he exerts is not so powerful but it is relentless and unceasing and no oyster muscle can resist it for more than a few hours. Presently the sh.e.l.l gapes open. The starfish lumbers over and commences to feed, other starfish often coming to enjoy the feast."

"And are there starfish enough to injure the beds?"

"Myriads of them. A starfish is not easy to kill, moreover, because if any of the arms are cut off he will grow a new one."

"How do the oystermen fight them?"

"By catching them in tangles. The snarled cotton waste does no harm to the oyster, but, as it is pulled over the bed, picks up hundreds of starfish and sea-urchins. Up-to-date vessels engaged in that work have a vat of boiling water on deck, into which the tangle is plunged when it is pulled up from the bottom. This kills the starfish and is a great gain over the old system of picking them out of the tangle by hand.

"But the worst of all the oyster's enemies," the director continued, "and the one on which I am working, is the oyster-drill. At least eighty per cent of the possible oyster crop is destroyed by this sea-snail.

This creature, usually about half an inch long, crawls on an oyster--usually a young one--and with a rasp-like tongue files a hole in the sh.e.l.l, through which it sucks the juices out of the oyster. The only thing that keeps the oyster-drill in check at all is that as soon as it is big enough for a younger drill to climb on its sh.e.l.l, it is apt to suffer the same fate. It is a case of reversed cannibalism, the stronger falling to the weaker."

"What can be done to stop it?"

"Nothing so far," said the director; "that is my chosen problem. Because the drill prefers the thin-sh.e.l.led mussel to the thicker-sh.e.l.led oyster it has been suggested that mussels should be planted outside oyster-beds, so that the drills would stay there. But the cure would be worse than the disease, for the mussels would spread over the oyster-bed and the drills with them, since they would have so excellent a breeding ground. No, the problem is still unsolved, and the people of the United States are looking to the Bureau of Fisheries to solve it. The Bureau has given it to me. That's the fascination of this work, that on your own toil and your own skill and ingenuity a factor of world-wide importance may depend."

"Perhaps----"