estral memories.

He had understood perfectly well his master's order that he leave them
alone. And he had been disappointed by it. He himself had not known
clearly what it was he would have liked to do to them. But he had known
he and they ought to have some sort of relationship. And then at the
gesture and the snarled command of "Go get them!" some closed door in
Chum's mind had swung wide, and, acting on an instinct he himself did
not understand, he had hurled himself into the gay task of rounding up
the flock.

So, for a thousand generations on the Scottish hills, had Chum's
ancestors earned their right to live. And so through successive
generations had they imbued their progeny with that accomplishment
until it had become a primal instinct. Even as the unbroken pointer of
the best type knows by instinct the rudiments of his work in the field
so will many a collie take up sheep herding by ancestral training.

There had been nothing wonderful in Chum's exploit. Hundreds of
untrained collies have done the same thing on their first sight of
sheep. The craving to chase and slay sheep is a mere perversion of this
olden instinct; just as the disorderly "flushing" and scattering of
bird coveys is a perversion of the pointer or setter instinct. Chum,
luckily for himself and for his master's flock, chanced to run true to
form in this matter of heredity, instead of inheriting his tendency in
the form of a taste for sheep murder.

The first collie, back in prehistoric days, was the first dog with the
wit to know his master's sheep apart from all other sheep. Perhaps that
is the best, if least scientific, theory of the collie's origin.

But to Link Ferris's unsophisticated eyes the achievement was all but
supernatural, and it doubled his love for the dog.

That afternoon, by way of experiment, Ferris took Chum along when he
went to drive the sheep back from pasture to the fold. By the time he
and the dog were within a hundred yards of the pasture gate Chum began
to dance, from sheer anticipation; mincing sidewise on the tips of his
toes in true collie fashion, and varying the dance by little rushes
forward.

Link opened the crazy gate. Waiting for no further encouragement the
dog sped into the broad field and among the grazing sheep that were
distributed unevenly over the entire area of the lot.

Ordinarily--unless the sheep were ready to come home--it was a matter
of ten or fifteen minutes each evening for Link to