Some kinds of monkeys have established a facial expression, accompanied with a laughing noise, which is so like the human that we might charge them with being entertained at the practical jokes which they pass upon each other, or over some obscurer sense of sylvan incongruity. We can see, at least, that Nature was preparing in them the nervous connections which men employ to transmit their pleasurable emotions; as the flexible plants which dangle by the streams and chasms of the Andes are woven by his after-thought to span the intervals, and the good cheer of humanity passes to and fro. The respiratory nerves radiate from their centre in the medulla oblongata, the place to which the brain must transmit the first shock of the surprise which ends in smiling and laughing. Thence it is transmitted to the heart and diaphragm, quickening the action of the one, and setting the other in motion, at the same instant climbing to engage the facial nerves in sympathy; then the orbicular muscles retract, forcing the cheek up towards the eye, and tightening the muscles which surround the eyelid. All our passions appear to claim the respiratory nerves for outward expression. They are a signal corps which communicate by hoisting the blush, the smile; by letting fall the tear, by the exhalation of a sigh, by the explosions of laughter. The life-breaths of joy and grief tend primitively to the lungs, and they voice the mother-tongue of all emotions. I have often wondered how animals can avoid being struck with the differences which exist among themselves, so much more salient and intrusive than among the races of men, in shape, gestures, tones, and habits. What a wide range of Nature's curious freakery a forest has, or a district of country like those plains and thickets of Africa, where the natives dig their great pit and organize a monster drive! Into it falls every thing which cannot escape to either side. The giraffe, elephant, gnu, antelope, hartbeest, zebra, jackal,--think of the commingling of strange discrepancies thus suddenly collected! Were it not for the panic which prevails, and the accidents to life and limb, one would suppose that they ought to be aware of Nature's whims in themselves, and to narrowly escape inventing amusement. But curiosity and aversion probably exhaust the speculative possibilities of animals in this direction. It is true, we occasionally hear of happy families, like that of the prairie-dog who has an owl and a rattlesnake to share his housekeeping, which they do with zest; for they have established a taste for the young of the prairie-dog, and they hire his tenement only with an eye to business.