A B Y, A Y, A B, X Y and B do not occur at all, some of them for obvious reasons, Occasionally there is an instructive progressive evolution expressed in these formula; for instance Phaethon, in various other respects the lowest of the Steganopodes, has A X Y, Sula and Phalacrocorax have A X, Fregata, the most specialized of these birds, has arrived at the reduced formula A.

Reduced.) Bering Island, Phalacrocorax perspicillatus; and how long will the flightless cormorant, Ph.