Jack pointed with a hand that trembled from fright. Staring at them through the thick glass of the bull's-eye the boys beheld the most hideous sea monster they had yet encountered.
It seemed to be a vast circular mass of flesh, twenty feet in diameter, and, in the middle were two openings each three feet across. They were like big holes, and, at the farther end of them could be seen two unblinking eyes. In the centre was a horrible mouth, armed with a triple row of teeth.
Down below there was a short body, at the end of which was a smaller disk, armed with a sharp horny point.
"What is it?" asked Jack in a whisper.
"I don't know," replied Mark.
A moment later Mr. Henderson came up the companionway into the tower. He caught one glimpse of the monster.
"It is the great sucker of the polar seas!" he exclaimed. "Quick! Speed up the engine! If that one, and the mates of it, fasten on to us we will have trouble!"
He pressed the signal that connected with the engine room, and told Washington to start the engine at its greatest power. The next instant the ship throbbed and trembled under the vibrations of the big screw.
"We may escape!" cried the professor.
As he spoke the ship seemed to come to a sudden stop. The engine could still be felt moving, and the big screw still churned the water to foam in the tunnel, but the craft was stationary.