when young and growing
rapidly. Mr. Trouvelot tells us in the "American Naturalist" that the
food taken by a single American Silk-worm in fifty-six days is equal to
eighty-six thousand times its primitive weight! On the other hand, after
the insect has finished its transformations, it either takes no food at
all, as in the May fly, or merely sips the honey of flowers, as in the
butterfly, while the June beetle and many others like it eat the leaves
of trees, and the tiger and ground beetles feed voraciously on other
insects.

_How Insects Walk._ In man and his allies, the vertebrates, the process
of walking is a most difficult and apparently dangerous feat. To
describe the mechanics of walking, the wonderful adaptation of the
muscles and bones for the performance of this most ordinary action of
life, would require a volume. The process is scarcely less complex in
insects. Lyonnet found 3,993 muscles in a caterpillar, and while a large
proportion belong to the internal organs, over a thousand assist in
locomotion. Hence the muscular power of insects is enormous. A flea will
leap two hundred times its own height, and certain large, solid beetles
will move enormous weights as compared to the bulk of their bodies.

[Illustration: 8. Larva of a beetle (Photuris).]

In walking, as seen in the accompanying figure (Fig. 8), three legs are
thrown forward at a time, two on one side and one on the other.

Flies and many other insects can walk upside down, or on glass, as
easily as on a level surface. A fly's foot, as in most other insects,
consists of five joints (tarsal joints), to the last one of which is
appended a pair of stout claws, beneath which is a flat, soft, fleshy
cushion or pad, split into two (sometimes three) flaps, beset on the
under surface with fine hairs. A part of these hairs are swollen at the
end, which is covered with "an elastic membranous expansion, capable of
close contact with a highly polished surface, from which a minute
quantity of a clear, transparent fluid is emitted when the fly is
actively moving." (T. West.) These hairs are hence called holding, or
tenent, hairs. With the aid of these, but mainly, as Mr. West insists,
by the pressure of the atmosphere, a fly is enabled to adhere to
perfectly smooth surfaces. His studies show the following curious facts.
"That atmospheric pressure, if the area of the flaps be alone
considered, is equal to just one-half the weight of a fly. If the area
covered