which interest me," remarked
George, gazing at John, as he continued: "Why should the inscriptions
have been marked on the skulls?"

John slowly shook his head, as he looked at Clifford. The latter gazed
vacantly into space, as though reflecting, and finally said: "I do not
know."

It will be remembered that when Walter entered the Professor's room,
where Clifford was lying, he appeared to be startled at the sight of
the skulls. The copper box which held one of them was in the adjoining
room.

During the foregoing conversation Walter was mute, nor did he appear
interested in the question propounded by George.

"It seems most curious to me that the skull taken from the copper box
has the inscription on the right side, whereas the other one has them on
the left side," observed Harry.

John and George saw the immediate change in Walter's face while Harry
was speaking. His agitation was now plain to all, and the perspiration
began to appear on his forehead.

John leaned forward as he said: "Do you know?"

Walter started at the vehemence of the question, and threw back his
head, as he answered: "Did you find the copper box?"

"Yes," responded John, with a look of triumph.

Walter's features relaxed, and he seemed to sink down, as he gazed about
him with a final look of despair.

"Then the quest is ended!" he muttered.

"What do you mean? Explain!" demanded John.

"When I began the search for the treasure of the caves, I was the owner
of the original document written by Juan Guiterez before he died in the
Spanish prison. Three attempts had been made to find the island, which
contained the secret, and that secret was in the copper box which told
of the places and the locations of the other caves. In each case the
quest failed, and all perished. The peculiar significance arises from
the fact that the only directions were given on a human skull by
Guiterez himself, who declared that two of the skulls would have the
inscriptions on the left side, while the one with the cryptic signs on
the right side would be accompanied by the descriptions of the locations
of all the Caves on the different islands."

"But why should there be three skulls?" asked George, in great
eagerness.

"There were three attempts, each resulting in death. The skull is
emblematic of death."

"Will you tell us why you tried to avoid Clifford, and were startled at
the sight of the skulls?" asked John.

"If, as you say, you have found the