4), pigeons, gulls, plovers, rails and penguins, have the vomer pointed in front while the maxillo-palatines are free, leaving a fissure between the vomer and themselves.
The short feet of the penguins are an adaptation.
The only really aberrant modifications of the wing-muscles are found in the Ratitae, where they are, however, all easily explained by reduction, and in the penguins, where the wings are greatly specialized into blades for rowing with screw-like motions.
Finally divers, auks and penguins, according to him, form the last term in the series, and it seems fit to him that they should be regarded as forming a separate order.
The sixth order, Natatores, consists of all the birds that habitually swim and a few that do not, containing 6 " cohorts ": Longipennes and Pygopodes with 3 families each; Totipalmatae with I family; Tubinares with 3 families; Impennes with I family, penguins; and Lamellirostres with 2 families, flamingoes and ducks.