The Ravens possess a vigorous and sustained flight; they have a keen sense of smell and excellent vision. By exercising these latter qualities they quickly learn where food is to be obtained, and as they wing towards it they constantly utter their cry, as if inviting their companions to join them; this croak, as it is called, is harsh and dissonant. Their plumage being of a sombre black, and their voice so unmusical, have doubtless been the reasons why they have long been considered Birds of ill omen. When taken young, they are tamed with great facility, for they will neither rejoin their own race nor desert the neighborhood where they have been kindly treated. True, they may go into the fields to seek for food, but when the increasing shadows predict the approach of night, their familiar resting place in the house of their protector will be sought. They become much attached to those who take notice of them, and will recognize them even in a crowd. THE DIPPERS. [Illustration: DIPPERS OR WATER WRENS.] The Dippers or Water Wrens have straight and slender bills; large and stout toes, furnished with strong hooked claws, and short wings and tails. The decidedly aquatic habits of these Birds form a curious exception to the rest of the Sparrow family. They live constantly on the edge of the water, or in the water itself, hunting for the Insects which constitute their food. Although their toes are not webbed, they may often be noticed diving and moving about under water, by extending their wings and using them as fins. They are frequently seen flying along streams, and catching the winged Insects skimming over the surface of the water. They build their nests along the banks of mountain streams, and thrive in great numbers in such rocky countries as the Alps, Pyrenees, and other mountain chains in the south, west and north of Europe. Fishes. [Illustration: FLYING-FISH.] THE numerous Fishes that inhabit the waters all over the globe are divided into two great groups—the Cartilaginous Fishes, with their framework made up of bones in the form of cartilage or gristle, and the Osseous, or bony Fishes. These large groups are sub-divided in a most puzzling manner by many Naturalists. The long Latin and Greek names used to classify these groups and smaller families are so much more difficult to remember than are the divisions of the great group of Mammals, that we will entirely discard all these derivations and explanations, using only the common English names for grouping them according to their peculiarities of form, the arrangement of the gills, the number and form of their fins, etc., etc.