"Well, it may not have been a big one, but you were in a mighty hurry to get to the aeroplane," said Billy with a grin.
"That was so that I could get my volcano monster's flea back safe and sound," exclaimed the man of science. "See here."
He took from his pocket and held up a small bottle.
"Look there," he exclaimed in triumph.
"Well," said the others, who, all but Frank, who was steering, were regarding the naturalist.
"Well," he repeated somewhat querulously, "don't you see it?"
"See what?" asked Billy, after a prolonged scrutiny of the bottle.
"Why, the flea, the little insect I caught in the shaggy fur of the volcano monster?"
"No," cried both boys simultaneously.
The professor gazed at the bottle in a puzzled way.