.

"Gee! aren't its eyes big?"

"And beautiful, too," said the guide. "They are made up of thousands of
facets (a facet is just a small, plain surface) as many as thirty
thousand facets in one eye. Some look up, some look down, some look out,
some look in; so that there is nothing that escapes the sight of this
hawk of the air. Look at the wings on this fellow, and look at the
picture I drew for you of the nymph. Well, this fellow's wings begin in
the nymph as tiny sacs, or pads, made by the pushing out of the wall of
the body. Running all through between the two layers of the wing are
thickened lines of chitin, which divide and subdivide, forming this fine
network. In the new wing, protected by these thickenings, are air-tubes,
which divide and branch into all parts of the wing. But as the wing
reaches its full growth most of the air-tubes die." The guide paused.
"We are talking too much and fishing too little. Time to go on. Put out
the fire, boys. Be sure that it's out. Run water all around it. Now
we're off!" And up, up, up the brook they went.

VII

THE SWIMMING-POOL

Two or three days after the fishing expedition the boys had gathered
together at the swimming-pool, Ben Gile with them. They had been racing,
and climbing trees, and were very warm. "Come, boys," said the guide,
"let's sit down a minute before you go into the water. It won't do to
bathe when you're too warm. Look round on the stones under the water and
see what you can find."

"Look at this," called Peter; "it's just like a sponge."

"It is a fresh-water sponge."

"I didn't suppose sponges grew in these parts at all," said Jimmie.

"Oh yes, there are many of them in the ponds."

"See this, sir," shouted Jack; "what funny little legs it has!"

"That's a May-fly or shad-fly nymph. He was hiding carefully under that
stone and keeping out of the way of the dragon-fly nymph, who would so
gladly gobble him up."

"It's prettier," said Jimmie, "than that dragon-fly nymph you drew a
picture of."

"So it is. See, here on each side of its body are these fine little
gill-plates, moving, moving, moving, so that they may get as much fresh
air as possible out of the water. Each gill-plate is a tiny sac, and
within these are the fine branches of the air-tubes. It's wonderful the
way these creatures breathe."

"Don't they breathe just the way we do?" asked Jack.

"No; throughout the body of an insect is a system of tiny white tubes.
Some da