with leaves and other decaying vegetable matter. The fermentation of
these leaves produces heat and so does for the alligator's eggs what
sitting does for those of hens and other birds: the mother deputes her
maternal functions, so to speak, to a festering heap of decomposing
plant-refuse. Nevertheless, she loiters about all the time, like
Miriam round the ark which contained Moses, to see what happens; and
when the eggs hatch out, she leads her little ones down to the river,
and there makes alligators of them. This is a simple and relatively
low stage in the nursery arrangements of the big lizards.

The African crocodile, on the other hand, goes a stage higher. It lays
only about thirty eggs, but these it buries in warm sand, and then
lies on top of them at night, both to protect them from attack and to
keep them warm during the cooler hours. In short, it sits upon them.
When the young crocodiles within the eggs are ready to hatch, they
utter an acute cry. The mother then digs down to the eggs, and lays
them freely on the surface, so that the little reptiles may have space
to work their way out unimpeded. This they do by biting at the shell
with a specially developed tooth; at the end of two hours' nibbling
they are free, and are led down to the water by their affectionate
parent. In these two cases we see the beginnings of the instinct of
hatching, which in birds, the next in order in the scale of being, has
become almost universal.

I say _almost_ universal, because even among birds there are a few
kinds which have not to this day progressed beyond the alligator
level. Australia is the happy hunting-ground of the zoölogist in
search of antiquated forms, elsewhere extinct, and several Australian
birds, such as the brush-turkeys, still treat their eggs essentially
on the alligator method. The cock birds heap up huge mounds of earth