The beak of a goose, as I may add, might also be
converted by small changes into one provided with prominent, recurved
teeth, like those of the Merganser (a member of the same family), serving
for the widely different purpose of securing live fish.
Returning to the whales. The Hyperoodon bidens is destitute of true teeth
in an efficient condition, but its palate is roughened, according to
Lacepede, with small unequal, hard points of horn. There is, therefore,
nothing improbable in supposing that some early Cetacean form was provided
with similar points of horn on the palate, but rather more regularly
placed, and which, like the knobs on the beak of the goose, aided it in
seizing or tearing its food. If so, it will hardly be denied that the
points might have been converted through variation and natural selection
into lamellae as well-developed as those of the Egyptian goose, in which
case they would have been used both for seizing objects and for sifting the
water; then into lamellae like those of the domestic duck; and so onward,
until they became as well constructed as those of the shoveller, in which
case they would have served exclusively as a sifting apparatus. From this
stage, in which the lamellae would be two-thirds of the length of the
plates of baleen in the Balaenoptera rostrata, gradations, which may be
observed in still-existing Cetaceans, lead us onward to the enormous plates
of baleen in the Greenland whale.
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