showed its back fin now and then, and twice over
droves of pigs started up out of the hot sand to make for cover. But
still there was no sign of inhabitant or opening in the reef, while
scores of tempting places were passed, all inviting to a naturalist, and
above all to Jack; vistas among the trees took his attention, and
valleys rising upward toward the higher parts of the mountain.

Upon one of these occasions, when he was sitting back in a deck-chair,
sweeping the side of the mountain with his glass, the doctor came up
behind him.

"Looking at the mountain?" he said.

"Yes; couldn't we get up there?"

"I vote we try," said the doctor. "Will you come?"

"Yes," cried Jack eagerly; "but we couldn't land and start now."

"Hardly," said the doctor, laughing. "We should have to start at
daybreak."

"What, to get up a little way like that?"

"Yes, to get up that little way," said the doctor, with a queer twinkle
of the eye. "Well, we don't seem to see anything likely to hinder our
landing to-morrow and having a good time at collecting. We must soon
get round to our starting-place. Let's ask the captain how far we have
come."

"Roughly speaking, nearly fifty knots," said the captain. "It's getting
well on toward six bells now, and we've been coming at a fair speed, and
are going a bit faster. I want to reach the anchorage before dark."

At one time this seemed to be doubtful, but just as the captain
announced his intention of dropping anchor for the night, Mr Bartlett
hailed him from above.

"I can just see the opening in the reef over that low strip of sand."

"How far off?"

"About a mile," was the reply; and the speed being increased, they
picked up the buoy they had left in the morning just as it was beginning
to grow dark, having completely circumnavigated the island.

"I say, Mr Bartlett," cried Jack suddenly, as the mate approached him,
and he pointed toward the shore. "Wasn't it just there that we killed
the sharks?"

"Yes; just there. Can you see any back fins?"

"No; but where's the wrecked canoe?"

The mate clapped his glass to his eye, and swept the shore for some
minutes.

"Could it have been carried out to sea?" said Jack excitedly.

"No; hardly possible."

"Then has it sunk?"

"No; it could not sink."

"Then what does it mean? We left it there."

"It means that the blacks have been and fetched it while we were away,"
said the mate, drawing a deep breath. "Just as Ca