hem. Not that I object to cats and dogs," he hastily
added, "but I think some other form of scientific activity might be
chosen. However, Professor Petersen was very peculiar, and, after all,
it was his money. Will you boys help me?"

"Indeed we will!" cried Jerry. "But how are we to go about it? What
part of France were the girls last in?"

"And what are their names?" Bob demanded.

"And what do they look like?" asked Ned.

"That last question I can answer first," said the professor. "I happen
to have recent pictures of them. They sent them to their uncle
following the deaths of their parents, and after the reconciliation,
and Professor Petersen left them to me, with certain other material,
documents and such, to aid me in the search. Here are the girls--their
names are Gladys Petersen and Dorothy Gibbs."

He reached in his pocket and took out a folded paper. As he opened it
he gave a start and hastily closed it again.

"That isn't it," he murmured. "Those are some dried specimens of
_ameba_ that I wish to study under a microscope."

"What are _ameba_?" asked Jerry. "Fish?"

"Not exactly," answered the professor with a smile, "though I secured
these from a little pond on the other side of the camp. _Ameba_ are
microorganisms of the simplest structure--a protoplasm which is
constantly changing in shape. Very interesting--very interesting
indeed, but not the pictures of the girls. Ah, here they are," he
added, as he replaced the first paper and took out a second. From the
folds of that he produced two unmounted photographs at which the boys
gazed with interest.

They saw the likenesses of two pretty girls in traveling costume, and
the pictures had, obviously, been snapped by an amateur at some
country place, for there was a barn and fields in the background.

"The girls took these pictures themselves, I understand," explained
the professor. "They sent them to their uncle."

"Which is which?" asked Jerry. "I mean which is Gladys and which is
Dorothy?"

"The names are on the reverse side of the photographs, I believe,"
said the professor, and so it proved.

"They are both pretty," observed Jerry.

"I rather fancy Gladys," murmured Ned.

"Dorothy seems real jolly," stated Bob.

"Here! None of that, young man, or I'll write to Helena Schaeffer,
and tell her how you're carrying on!" warned Jerry, shaking a finger
at his stout chum.

"Aw, you----" began Bob.

But at that moment there came an interruptio