These migratory birds frequent reedy streams and stagnant waters in summer, being companionable, though not gregarious; hard weather, however, drives them to the sea. They walk fairly well, though awkwardly, and sit upon the whole metatarsus; but the chicks progress on "all fours," using the wings almost {54}as forefeet.[52] They fly straight and rapidly, with head and feet extended, but have difficulty in leaving the water; they dive at the slightest alarm, their quick sight enabling them to vanish below the surface at the flash of a gun, to reappear, with hardly a ripple, at a distance. Frequently it requires much patience to obtain a second view, as their bodies can be submerged to any extent, and at times the bill alone is exposed. In swimming they jerk the head and often rise vertically to shake their wings. They descend from the air with a splash and a glide, while in diving the feet alone act as oars, the young soon equalling their parents in this respect. The note is a harsh croak in the larger forms, a softer sound or whit-whit in the smaller; the food consists of fish when procurable, but small reptiles, amphibians, molluscs, crustaceans, insects, and vegetable matter are frequently added, and feathers of some size are constantly found in the stomach. The nest, a pile of aquatic weeds or rushes of varying bulk, is fixed among reeds, sedges, semi-natant masses of herbage, or, more rarely, upon low branches of trees or bushes verging upon the water. Should this rise higher, fresh materials are added. From three to six bluish-white eggs with a smooth chalky covering are laid in a slight depression above, but being covered with wet weeds by the female on leaving, soon become stained with brown. The bill is used in concealing them, nor does an invader's presence usually hinder the operation. Incubation lasts from twenty-one to twenty-four days. Both sexes are said to assist, and the mother carries the nestlings on her back, or even dives with them in that position. ORDER III. SPHENISCIFORMES. The Order Sphenisciformes, with its Sub-Order SPHENISCI, contains only those remarkable marine birds the Penguins (Fam. SPHENISCIDAE), the life of which is chiefly spent on the stormy waters of the Antarctic seas. Coupled by former writers with the Auks, their northern analogues, it has now been shown that the slight external similarity of the two groups is utterly misleading, the nearest allies of the primitive forms here treated being the Petrels on the one hand and the Divers and Grebes on the other. Their unique structure is correlated with very peculiar habits.