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 32 FORM AND HABIT: THE BILL. corolla. In the Tooth-billed Hummer {A?idrod(m) both mandibles arc finely serrate at the end, the upper one being also hooked, and the bird feeds on insects which it captures on the surface of leaves and other places. Among the Woodhewers {DendroeolajMidw) of South America there is fully as much variability, which reflects equally variable feeding habits. Some sjDecies have short, stout, straight bills, others exceedingly long, slender, curved ones. Fig. 18.— Serrate bill of Merganser, a fish- MergauSCrS, Ganucts, Au- eating bird, ('/a natural size.) . . ° ' t . t hingas, and other birds that catch fish by pursuing them under water, have sharply serrate mandibles, which aid them in holding their slippery prey. Some shore birds (Limicolce) use the bill as a probe, Fio. 19. — Probelike bill of Woodcock, showing extent to which upper mandi- ble can be moved, (^/s natural size.) when it may be six inches in length and straight, or curved downward. It has recently been learned that Fig. 20. — Recurved bill of Avocet. (2/3 natural size.) several of these probing Snipe, notably the Woodcock, have the power of moving the end of the upper mandi-