We thus see that a member of the duck family, with a beak constructed like that of a common goose and adapted solely for grazing, or even a member with a beak having less well-developed lamellae, might be converted by small changes into a species like the Egyptian goose-this into one like the common duck-and, lastly, into one like the shoveller, provided with a beak almost exclusively adapted for sifting the water; for this bird could hardly use any part of its beak, except the hooked tip, for seizing or tearing solid food.
Ikusten dugu, bada, ahate familiako espezie bat, mokoa antzar arruntarena bezala egina eta belarra jateko soilik moldatua duena, eta are xaflatxo ez hain garatudun mokoa duen espezie bat, aldaketa txikika Egiptoko antzarra bezalako espezie bilaka daitekeela; hau, berriz, ahate arruntarena bezalako, eta azkenez mokozabala bezelako espezie, ia soilik ura bahetzeko moldaturiko mokoz hornitua; izan ere txori honek nekez erabili ahal izanen luke bere mokoaren parte bat bera ere, punta makurra izan ezik, janari solidoa atzeman edo txikitzeko.