things and work in a particular way. These are termed "organs," and
the whole together is called "organic." And as it is universally
characteristic of them, this term "organic" has been very conveniently
employed to denote the whole of living nature,--the whole of the plant
world, and the whole of the animal world.

Few animals can be more familiar to you than that whose skeleton is
shown on our diagram. You need not bother yourselves with this "Equus
caballus" written under it; that is only the Latin name of it, and does
not make it any better. It simply means the common Horse. Suppose we
wish to understand all about the Horse. Our first object must be to
study the structure of the animal. The whole of his body is inclosed
within a hide, a skin covered with hair; and if that hide or skin be
taken off, we find a great mass of flesh, or what is technically called
muscle, being the substance which by its power of contraction enables
the animal to move. These muscles move the hard parts one upon the
other, and so give that strength and power of motion which renders the
Horse so useful to us in the performance of those services in which we
employ him.

And then, on separating and removing the whole of this skin and flesh,
you have a great series of bones, hard structures, bound together with
ligaments, and forming the skeleton which is represented here.

[FIGURE 1. (Section through a horse.)

FIGURE 2. (Section through a cell.)]

In that skeleton there are a number of parts to be recognized. The
long series of bones, beginning from the skull and ending in the tail,