does the same thing instantaneously, and as by a common impulse, whilst in the second, half acts in one way, and half in another, each appearing to have no doubt or hesitation as to what it ought to do! Again, how different is the conduct of the two field-assemblages. One rises, as with one thought, to join the flying birds. The other, as with one thought, remains standing. Unless, in each case, some signal of command has been given, then what a strange community of feeling in opposite directions is here shown. Where is the individuality that one would expect, and what is the power that binds all the units together?
"Are rooks led by an old and experienced bird?—which is, I believe, the popular impression, as embodied in a famous line of Tennyson, for which one feels inclined to fight. At first sight, the rising of a whole body of rooks (or any other birds) simultaneously, either from the ground or a tree, might seem to be most easily explained on the theory of one bird, recognised as the chief of the band, having in some manner—either by a cry or by its own flight—given a signal, which was instantly obeyed by the rest. But how—in the case of rooks—can any one note be heard by all amidst such a babel as there often is, and how can every bird in a band of some hundreds (or even some scores) have its eyes constantly fixed on some particular one amongst them, that ought, indeed, on ordinary physical and mechanical principles, to be invisible to the greater number? If, however, to meet this latter difficulty, we suppose that only a certain number of birds, who are in close proximity to the leader, see and obey the
