ment in favor of taking all the
gradual steps from flower to bird. By this time the main ideas are
firmly lodged, the child will readily draw his own conclusions as to the
rest; but there are one or two facts connected with the origin of the
bird which are of great value in fixing the idea of _necessity_ which is
at the foundation of all reproductive phenomena. Everything is as it is
because it is necessary that it should be so. In the frog the higher
development made necessary greater economy in the production of the egg
and the fertilizing cell, and this economy of material necessitated the
more certain fertilization of the egg.

In the bird a great step upwards has been taken. Here we have something
much more complex in every way. The frog was cold-blooded, comparatively
sluggish, and comparatively simple in structure. The bird is
warm-blooded, intensely active, and very much more complex both in
bodily structure and in mind development. Here the reproductive activity
is yet more economically conducted, and instead of thirty or more eggs,
the bird produces often not more than six in a season, and even a
smaller number if it is single-brooded, some eagles, for instance,
rearing only two young in a season. Naturally these few eggs must be
very carefully protected. Since they are not laid in the yielding medium
of water, they cannot have so soft a covering as the eggs of the fish or
frog, but are enclosed in a hard shell. This shell must of course be
formed before the egg is laid, and the egg must be fertilized before
the hard shell encloses it and thus makes forever impossible the
entrance of the fertilizing cell.

The ovaries of the bird are in the small of the back close to the
backbone, and there is a tube called the oviduct or egg-duct, leading
from the ovary down to the lower end of the intestine, which it enters.
There is no separate opening for the oviduct into the outer world.

There are two ovaries, with their oviducts, in the young bird, but these
are so small that it is very difficult indeed to find them. As the bird
approaches maturity, one ovary and its oviduct enlarge, and the ova,
which develop from the inside of the ovary just as the ovule develops
inside the flower ovary, also become large. Although the bird is born
with two ovaries, but one, usually, develops, generally the one on the
left side.

When the bird comes to maturity, there is born in it a yearning for home
and offspring. As the eggs de