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.