The middle and longest lamina in the Greenland whale is
ten, twelve, or even fifteen feet in length; but in the different species
of Cetaceans there are gradations in length; the middle lamina being in one
species, according to Scoresby, four feet, in another three, in another
eighteen inches, and in the Balaenoptera rostrata only about nine inches in
length. The quality of the whalebone also differs in the different
species.
With respect to the baleen, Mr. Mivart remarks that if it "had once
attained such a size and development as to be at all useful, then its
preservation and augmentation within serviceable limits would be promoted
by natural selection alone. But how to obtain the beginning of such useful
development?" In answer, it may be asked, why should not the early
progenitors of the whales with baleen have possessed a mouth constructed
something like the lamellated beak of a duck? Ducks, like whales, subsist
by sifting the mud and water; and the family has sometimes been called
Criblatores, or sifters. I hope that I may not be misconstrued into saying
that the progenitors of whales did actually possess mouths lamellated like
the beak of a duck. I wish only to show that this is not incredible, and
that the immense plates of baleen in the Greenland whale might have been
developed from such lamellae by finely graduated steps, each of service to
its possessor.
The beak of a shoveller-duck (Spatula clypeata) is a more beautiful and
complex structure than the mouth of a whale.
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