436 The Bird 
body between the thighs. Both sexes are provided with 
this contrivance during the breeding season, and relieve 
each other of the burden at intervals. 
“The gull tribe, however, are far more exposed to acci- 
dent and to enemies, both in adult life and as to their 
eggs and young, than are the penguins, petrels, and others 
mentioned above; and here the rule is from two (skuas) 
to four (gulls and terns) eggs in a nest. When we come 
Fic. 346.—Eggs of Ostrich, Cassowary, Hummingbird, and Hen, 
showing comparative size. 
to the shore- and marsh-birds—the plovers, snipe, sand- 
pipers, jacanas, all of which nestle on the ground, usually 
near the shore of the sea or lakes—we judge them to be 
exposed to about the average of dangers, since their nest 
complement is from four to six. The northern, tundra- 
loving cranes need raise few young, and hatch only two 
eggs; but when we come to the water-birds—the rails, 
gallinules, ducks, and geese—we find an extensive group 
