former occasion, when the
professor, coming to visit his friends at Camp Dixton, had been halted
on his way through the lines after some insects.

"I never thought of that," admitted the scientist. "I certainly
remember coming down here in the spring, but I forgot about the spy
business."

This was not surprising, since the professor seldom remembered for
very long anything not directly connected with his favorite study.

And so, with the snake in the box safely confined to the care of Pete
Bumps in the automobile, Professor Snodgrass went back to dine with
the colonel, while the three chums hastened to their delayed mess.

"You never know when he is going to turn up," remarked Ned.

"That's right," agreed Jerry. "I wonder what he's after now?"

They did not have long to wait before learning. Soon after mess they
saw the professor coming down their company street and, as they had a
brief respite from drills on account of the strenuous work of the
morning, the boys took him to a quiet spot and began to ask him
questions.

"But first of all, tell us if there is anything the matter?" begged
Jerry. "You look worried. Are you?"

"Yes," admitted the little scientist, "I don't mind admitting that I
am worried--and puzzled, too."

"What about?" asked Bob. "Ticula hasn't got loose, has she?"

"No, I went over to see, after dining with your colonel, whom I found
to be a most delightful man, though his ignorance of reptiles and
insects is painful. But, as I say, I assured myself of the safety of
Ticula. Pete has her in the auto."

"Then what's worrying you?" demanded Ned.

"Well, I have a problem to solve and I don't know how to do it," was
the answer.

"Has it anything to do with the war?" Jerry queried.

"Yes, it has," was the unexpected answer. "And now that you boys are
in the army and expect to go across to France soon, perhaps you can
help me. I'll tell you the puzzle I am trying to solve."

CHAPTER IV

A TWO-GIRL PROBLEM

Jerry Hopkins stretched himself lazily and comfortably out on the
grass under the shade tree where he and Bob and Ned had taken
Professor Snodgrass for a little talk. They were far removed from the
center of the camp, so the noise of the men drilling or at their
various occupations came but faintly.

"Do you mean that your problem has to be solved on the other side of
the water, Professor?" asked Jerry.

"Part of it has. And I am anxious to get across as soon as possible t