Turning to another group of the same family. In the Egyptian goose
(Chenalopex) the beak closely resembles that of the common duck; but the
lamellae are not so numerous, nor so distinct from each other, nor do they
project so much inward; yet this goose, as I am informed by Mr. E.
Bartlett, "uses its bill like a duck by throwing the water out at the
corners." Its chief food, however, is grass, which it crops like the
common goose. In this latter bird the lamellae of the upper mandible are
much coarser than in the common duck, almost confluent, about twenty-seven
in number on each side, and terminating upward in teeth-like knobs. The
palate is also covered with hard rounded knobs. The edges of the lower
mandible are serrated with teeth much more prominent, coarser and sharper
than in the duck. The common goose does not sift the water, but uses its
beak exclusively for tearing or cutting herbage, for which purpose it is so
well fitted that it can crop grass closer than almost any other animal.
There are other species of geese, as I hear from Mr. Bartlett, in which the
lamellae are less developed than in the common goose.
We thus see that a member of the duck family, with a beak constructed like
that of a common goose and adapted solely for grazing, or even a member
with a beak having less well-developed lamellae, might be converted by
small changes into a species like the Egyptian goose--this into one like
the common duck--and, lastly, into one like the shoveller, provided with a
beak almost exclusively adapted for sifting the water; for this bird could
hardly use any part of its beak, except the hooked tip, for seizing or
tearing solid food.
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