292 VERTEBRATE ANIMALS. 
mots and Grebes, have rudimentary, or at any rate small, 
wings, and are all more at home in the water than upon land. 
The Gulls, Terns, and Petrels, on the contrary, are all birds of 
powerful flight, and some of them, such as the Albatross, are 
habitually found hundreds of miles from the nearest land. 
The Pelicans, with their allies the Cormorants, Frigate-birds, 
and Darters, are excellent flyers, and also not uncommonly 
perch on trees, which few Natatorial birds do. They are dis- 
tinguished by having the hinder toe directed inward, and united 
to the innermost of the front toes by a continuous membrane. 
The Gannets, Ducks, Geese, and Swans, have the bill very much 
flattened and covered by a soft skin. The edges of the bill are 
also furnished with a series of transverse plates, which form a 
kind of fringe or “strainer,” by means of which these birds sift 
the mud in which they habitually seek their food. 
ORDER II. GRALLATORES.—The Wading Birds for the most 
part frequent moist situations, such as marshes and shallow 
ponds, the shore of the sea or the banks of rivers or lakes, 
Fig. 156.—Grallatores. A, Leg and Foot of Curlew ; B, Head of Snipe ; 
C, Beak of Avocet. 
though some of them keep entirely, or almost entirely, to the 
dry land. In accordance with their semi-aQuatic, amphibious 
habits, the Waders are distinguished by the great length of 
their legs—the increase in length being chiefly due to the 
elongation of the tarso-metatarsus. The legs (fig. 156, A) are 
