teen years, though there is
no reason to worry if a girl does not menstruate for a number of years
later. In warm climates the age of puberty is from two to four years
earlier than in more temperate climates.

THE FUNCTION OF THE OVARY.--Just what takes place in each ovary when it
is ripe is best explained by likening an ovary to an orange,--though of
course the ovary is very much smaller than an orange, as was previously
noted. If you make a cut in an orange and squeeze it, you express some
of its juice and most likely you will also express one or more seeds.
The seeds of the ovaries are called "ovules," and the process by which
it expresses them is called "ovulation." Of course there is no actual
squeezing of the ovary,--the ovules grow in the ovary, and as they ripen
they come to the surface, and when actually ripe, the part of the
surface of the ovary to which they come, opens up (like a flower
unfolding when in bloom), and they fall out. The ovule we may regard as
the human female egg, and one ripens and falls out every twenty-eight
days.

When the egg falls out of the ovary it falls into the tube which carries
it into the womb. This tube you will remember is called the fallopian
tube. The ovule or egg is now in the cavity of the womb where we will
leave it for the present.

THE FUNCTION OF THE WOMB.--While these changes are going on in the
ovary, the womb is also preparing itself for its share of the work. The
lining or internal surface of the womb is composed of mucous membrane,
much the same as the interior lining of the mouth and throat. This
lining becomes congested with blood, and is so intensely swollen at the
time when the ovule or egg reaches the womb, that it is ready to rupture
and bleed all over its surface. Just whether it will rupture and bleed,
depends upon whether the egg is going to grow into a child or not. If it
is not going to grow into a child, it immediately bleeds freely, and
continues to bleed, until the whole lining of the womb and egg is passed
out into the outer world. This takes four or five days and constitutes
"menstruation." After menstruation is over, the womb begins again to
prepare itself for the coming of the next ovule or egg, and as this
occurs every twenty-eight days, menstruation is commonly termed the
"monthly periods."

WHY MENSTRUATION OCCURS EVERY TWENTY-EIGHT DAYS.--The reason why the
womb does this every twenty-eight days is because it is impossible to
tell just whe