ticated and for hundreds of years
kept as a barnyard Duck."

"River Ducks?" questioned Rap; "then are there different kinds of Ducks
for rivers and lakes, and for salt water?"

"There are indeed many kinds of Ducks," said the Doctor, "all of which
have easy marks of identification in the beauty-spot on the wings, and
many other points about the plumage, as well as the different shapes of
their heads, bills, and feet. Though all Wild Ducks, and Geese too,
belong to one general family, they are divided into separate groups like
cousins, instead of living in one household like brothers.

"Almost all Wild Ducks nest in the northern tier of States, or
altogether north of them; the hardier species stay with us as winter
visitors, but the others only stop to feed, as they follow the rivers
and coasts in their migrations.

"There was a beautiful Duck that had a nest last year in a tree up near
the logging camp; its feathers were as bright as if they had been
painted. That is the Wood Duck--one of the exceptions to the rule that
Wild Ducks nest on the ground like tame ones. Another kind, the Black
Duck, nests as usual on the ground, on a wooded island not far from the
one to which we are sailing."

"Will you please tell us why Ducks have such waddling legs?" begged Nat.

"Because the best legs to swim with are not the easiest to walk with."

At that moment the wind died down. The sails flapped once or twice, and
then hung loose; and the boat, instead of dashing along, began to drift
lazily, with an uncomfortable rolling motion, as the swell, borne in
from the ocean many miles away, crept under it.

"If the water does that much more, I shall soon be hungry," said Dodo,
looking a trifle sad and pressing her hands together over her waist.

"I quite agree with you," said Olive; "I know from having had the same
feeling before, that unless we eat some of these little salt biscuits,
and talk about something interesting, in a very few minutes you and I
will be sea-sick--which is the hungriest, emptiest sickness possible."

"I thought the feeling was a little more puffy than real hungriness,"
said Dodo, chewing her biscuit in great haste and having some trouble in
swallowing it.

"May not we men have some too?" asked the Doctor, looking drolly at the
boys, who were glancing longingly at the biscuits, but were too proud to
confess their feelings. "Not that we feel ill--oh, no! Merely for
company, you know.

"Now while you mu