ey put down their beaks into the mud and gathered it in their mouths;
and all the time they held their wings quivering up over their beautiful
blue backs, like a flock of butterflies just alighting with their wings
atremble.

So their plaster pit was just a mud-puddle. Yes, that is all; only it
had to be a particularly sticky kind of mud, which is called clay; for
the walls of their homes were a sort of brick something like that the
people made in Egypt years and years ago. And do you remember how the
story goes that the folk in Pharaoh's day gathered straws to mix with
the clay, so that their bricks would be stronger? Well, Eve and Petro
didn't know that story, but they gathered fibres of slender roots and
dead grass stems with their clay, which doubtless did their brick
plaster no harm.

[Illustration: _At Work in the Plaster Pit._]

Men brick-makers nowadays bake their bricks in ovens called kilns,
which are heated with fire. Eve and Petro let their brick bake, too, and
the fire they used was the same one the Egyptians used in the days of
Pharaoh--a fire that had never in all that time gone out, but had glowed
steadily century after century, baking many bricks for folk and birds.
Of course you know what fire that is, for you see it yourself every day
that the sun shines.

Every now and again Eve and Petro and all the rest of the swallow colony
left off their brick-building and went on a hunting trip. They hunted
high in the air and they hunted low over the meadow. They hunted afar
off along the stream and they hunted near by in the barnyard. And all
the game they caught they captured on the wing, and they ate it fresh at
a gulp without pausing in their flight. As they sailed and swirled, they
were good to watch, for a swallow's strong long wings bear him right
gracefully.

Why did they stop for the hunting flight? Perhaps they were hungry.
Perhaps their mouths were tired of being hods for clay they could not
eat. Perhaps the fresh plaster on the walls of their homes needed time
to dry a bit before more was added.

Be that as it may, they made the minutes count even while they rested
from their building work. For they used this time getting their meals;
and whenever they were doing that, they were working for the owner of
the barn, paying their rent for the house-lot on the wall by catching
grass insects over the meadow, and mosquitoes and horseflies and
house-flies by the hundreds, and many another pest, too.