o himself on behalf of some customer who ordered simply by
a code of ink dots. He was the man I had to find. The giant luna moths
helped to do it."

"I don't see where they come in at all," declared Dorr bluntly. "A moth
a foot wide couldn't crawl through a keyhole."

"No; nor do any damage if it did. The luna is as harmless as it
is lovely. In this case the moths weren't active agents. They were
important only as clues--and bait. Their enormous size showed Professor
Moseley's line of work; the selective breeding of certain forms of
life to two or three times the normal proportions. Very well; I had
to ascertain some creature which, if magnified several times, would be
deadly, and which would still be capable of entering a large keyhole.
Having determined that--"

"You found what it was?" cried Dorr.

"One moment. Having determined that, I had still to get in touch with
Professor Moseley's mysterious New York correspondent. I figured that he
must be interested in Professor Moseley's particular branch of research
or he never could have devised his murderous scheme. So I constructed
the luna moth advertisement to draw him, and when I got a reply from Mr.
Ross, who is a fellow-tenant of Mr. Dorr's, the chain was complete. Now,
you see where the luna moths were useful. If I had advertised, instead
of them, the lathrodectus, he might have suspected and refrained from
answering."

"What's the lathrodectus?" demanded both the hearers at once.

For answer Average Jones took a letter from his pocket and read:

BUREAU OF ENTOMOLOGY, U. S. DEPARTMENT OF AGRICULTURE, WASHINGTON, D.
C., April 7

MR. A. V. R. JONES,

Astor Court Temple, New York City.

DEAR Sir,

Replying to your letter of inquiry, the only insect answering your
specifications is a small spider Lathrodectus mactans, sometimes
popularly called the Red Dot, from a bright red mark upon the back. Rare
cases are known where death has been caused by the bite of this insect.
Fortunately its fangs are so weak that they can penetrate only very
tender skin, otherwise death from its bite would be more common, as the
venom, drop for drop, is perhaps the most virulent known to science.

This Bureau knows nothing of any experiments in breeding the
Lathrodectus for size. Your surmise that specimens of two or three times
the normal size would be dangerous to life is undoubtedly correct, and
selected breeding to that end should be conducted only under adequate
scienti