7. All birds become more noisy at the season of coition. Some utter a cry when they are fighting, as the quail; others when they are going to fight, as the partridge; or when they have obtained a victory, as the cock. In some kinds both male and female sing, as the nightingale; but the female nightingale does not sing while she is sitting or feeding her young: in some the males alone, as the quail and the cock; the female has no voice. Viviparous quadrupeds utter different voices; none can speak--for this is the characteristic of man, for all that have a language have a voice, but not all that have a voice have also a language. 8. All that are born dumb, and all children, utter sounds, but have no language; for, as children are not complete in their other parts, so their tongue is not perfect at first; it becomes more free afterwards, so that they stammer and lisp. Both voices and language differ in different places. 9. The voice is most conspicuous in its acuteness or depth, but the form does not differ in the same species of animals; the mode of articulation differs, and this might be called speech, for it differs in different animals, and in the same genera in different places, as among partridges, for in some places they cackle, in others whistle. Small birds do not utter the same voice as their parents, if they are brought up away from them, and have only heard other singing birds. For the nightingale has been observed instructing her young, so that the voice and speech are not naturally alike, but are capable of formation. And men also have all the same voice, however much they may differ in language. The elephant utters a voice by breathing through its mouth, making no use of its nose, as when a man breathes forth a sigh; but with its nose it makes a noise like the hoarse sound of a trumpet. CHAPTER X. 1. Concerning the sleep and wakefulness of animals. It is quite manifest that all viviparous animals with feet both sleep and are awake; for all that have eyelids sleep with the eyes closed; and not only men appear to dream, but horses, oxen, sheep, goats, dogs, and all viviparous quadrupeds. Dogs show this by barking in their sleep. It is not clear whether oviparous animals dream, but it is quite plain that they sleep. 2. And so it is in aquatic animals, as fish, the malacia, the malacostraca, the carabi, and such like creatures. The sleep of all these animals is short: it is plain that they do sleep, though we can form no conclusion from their eyes, for they have no eyelids, but from their not being alarmed; for if fish are not tormented with lice, and what are called psylli, they may be captured without alarming them, so that they can be even taken with the hand. And if fish remain at rest during the night a great multitude of these creatures fall upon and devour them.