Their habits are all nearly alike; but to one species of Grey Squirrel belongs a habit as distinct as it is singular. This is their habit of collecting together in immense flocks of many thousands, and migrating over vast tracts of country, crossing broad rapid rivers, and staying at no obstacle. The object of this migration is not known, only that it appears to be the result of some impulse--such as excites to a similar movement the springboks of South Africa, the buffaloes of North America, and the passenger pigeons. In Europe the squirrel is represented by the Common Squirrel of our own woods, and which is found throughout the whole of Northern Europe and Asia, wherever there are trees. Although of a reddish colour in England, as well as in France, it assumes different hues, according to the different countries it inhabits; and in the more northern latitudes it is quite grey. Another European species, distinct from the English squirrel, is a denizen of the Pyrenees and the Alps of Dauphine. The Palm Squirrel is a beautiful species belonging to the tropical parts of Africa and India, and dwelling principally upon the palm trees--as its name imports. Another, known as the Barbary Squirrel, belongs to North Africa, and is also a dweller upon palm trees. The largest, and perhaps the most richly-coated of the tribe, is the Malabar Squirrel of India, which is as large as a domestic cat. It also haunts among palm trees, and is fond of the milk of the cocoa-nut, either in a liquid or solid state. There are squirrels also in Eastern Africa. India has several species, and the great islands of Madagascar, Ceylon, Java, Borneo, Sumatra, etcetera, have each one or more species of large and beautiful squirrels. The _Ground Squirrels_ differ from the true squirrels in several respects, though the chief difference lies in the fact that the former make their nest or lair upon the ground, while the latter universally lodge themselves aloft among the branches. The Ground Squirrels can climb, and appear to ascend trees almost as nimbly as their congeners; but they rarely do so unless when pursued, and then but seldom go beyond the lower forks or branches. Their nest is usually in some hole or cavity among the roots, though several species have been lately discovered in rocky regions, dwelling in the crevices of rocks. They approach in habits to the marmot tribe, and seem to link the tree squirrels with these last. Usually, these ground squirrels are striped longitudinally with black, red, and white stripes, giving them a fine appearance; and the species are of different dimensions, from that of the ordinary squirrel to the size of a mouse. In America, for a long time, but one kind was supposed to exist; but latterly a great number of species have been observed and described: denizens of the far West--of the prairies, and remote valleys of the Rocky Mountains.