sts by this simple means. An ounce to each fifteen square feet
of water-surface is all that is required, though the oiling needs to be
repeated carefully several times during the season.

But what of the eggs? They require no air, and it was found impossible
to poison them without simply saturating the water with powerful
poisons; but an unexpected ally was at our hand. It was early noted that
mosquitoes would not breed freely in open rivers or in large ponds or
lakes, but why this should be the case was a puzzle. One day an
enthusiastic mosquito-student brought home a number of eggs of different
species, which he had collected from the neighboring marshes, and put
them into his laboratory aquarium for the sake of watching them develop
and identifying their species. The next morning, when he went to look at
them, they had totally disappeared. Thinking that perhaps the laboratory
cat had taken them, and overlooking a most contented twinkle in the
corner of the eyes of the minnows that inhabited the aquarium, he went
out and collected another series. This time the minnows were ready for
him, and before his astonished eyes promptly pounced on the raft of eggs
and swallowed them whole. Here was the answer at once: mosquitoes would
not develop freely where fish had free access; and this fact is our
second most important weapon in the crusade for their extermination. If
the pond be large enough, all that is necessary is simply to stock it
with any of the local fish, minnows, killies, perch, dace, bass,--and
presto! the mosquitoes practically disappear. If it be near some larger
lake or river containing fish, then a channel connecting the two, to
allow of its stocking, is all that is required.

On the Hackensack marshes to-day trenches are cut to let the water out
of the tidal pools; while in low-lying areas, which cannot be thus
drained, the central lowest spot is selected, a barrel is sunk at this
spot, and four or five "killie" fish are placed in it. Trenches are cut
converging into this barrel from the whole of the area to be drained,
and behold, no more mosquitoes can breed in that area, and, in the
language of the day, "get away with it."

Finally, most consoling of all, it was discovered that, while the
ordinary _Culex_ mosquito can breed, going through all the stages from
the egg to the complete insect, in about fourteen days, so that any
puddle which will remain wet for that length of time, or even such
exceedingly