The words flew like wild-fire, and off the crowd rushed--men, boys,
burgomaster, and watchmen, just in time to capture the traitor and to
drive back the enemy.

[Illustration: "'What is it?--a fire? Speak, boy!'"]

So his father had been right after all, and Ulrich's bit of work had
been ready for him, and nearer than he thought. And he did his best, and
doing his best saved the town. For help did come, and Ulrich was thanked
by the Emperor himself, who put him under the care of his own doctor.
The doctor, although he was not able quite to cure him, did him so much
good that he was able in the course of time to walk without a crutch.

E. W. GRIERSON.

[Illustration:

Fig. 1.--Aphis, showing "Tracheae" (greatly magnified).
Fig. 2.--"Tracheal Filaments" of Aphis (greatly magnified).
Fig. 3.--"Spiracles" of Water Beetle (greatly magnified).
Fig. 4.--Section of Crayfish, showing gills (magnified).]

INSECT WAYS AND MEANS.

VII.--HOW INSECTS BREATHE

Animal life cannot be sustained without breathing, though, strange as it
may seem, many of the lower animals have no special breathing organs. By
breathing, we mean supplying the body with the life-giving oxygen
contained in the air. Animals which live in the water breathe by taking
in the oxygen held in solution in the water.

In the simplest animals which live in water, the body is only a small
'blob' of jelly, so small that the oxygen passes directly into the body.
The bodies of some worms are so delicate that the oxygen easily passes
through the outer layers and mixes with the blood within.

In more complicated animals this life-giving gas is conveyed all over
the body by means of the blood, which is brought into contact with the
water, or the air, by structures known as gills. In the crayfish, for
example, the gills are placed above and rise from the bases of the legs,
being saved from injury by a broad shield lying behind the head. (In
fig. 4 this shield has been cut away so as to show the gills, marked G,
which it really covers.) By means of the circulation of the blood, the
crayfish breathes. This blood is carried to the gills and bathed by a
constant stream of fresh water, which enters behind the covering and
shield, and passes forwards till it comes out on each side of the mouth.
The blood, thus refreshed by the oxygen in the water, is carried again
all over the body, and in its course loses more and more oxygen, and
becomes more and more charged wi