"Now, what's happened to him?" demanded Zeb, with a trace of impatience.
"I don't know, but he must be in trouble of some sort," cried Jack.
"Maybe it's another donkey," mischievously suggested Dick.
The cries were redoubled. They waited no longer but started off across the island on the run. Zeb carried his big forty-four revolver.
CHAPTER XXIX.
A MUD BATH.
The ground was rough and rocky but they made good time. Bursting through a screen of trees from beyond which came the professor's piteous cries, they received a shock.
The man of science was in the center of a large, round hole full of black mud that bubbled and boiled and steamed as if it were alive. All that was visible of the professor was the upper part of his body.