"It must be remembered," says Knight, "that irregularity is the general characteristic of trees, and regularity that of animals."--It would have been more correct to say that symmetry is this peculiar characteristic. There is little resemblance between the parts of one side; and it is symmetry which results from the uniform disposition of double parts, and from the regular division of single ones. Hence an agreeable impression is produced by the corresponding disposition and the exact resemblance of the eyes, of the eyebrows, of the ears, of the hemispheres of the bosom, and of the different parts of which the limbs are composed; and the forehead, the nose, the mouth, the abdomen, the back, are agreeably distinguished by means of the median line which divides them. It appears that the eye is pleased by the exactness of corresponding parts; and that symmetry is the first character of beauty in thinking beings. Occasional irregularity makes us better appreciate the importance of symmetry. The oblique direction of the eyes, squinting, twisting of the nose or lips, unequal magnitude of the hemispheres of the bosom, or unequal length of the limbs, disfigure the most beautiful person. But how does symmetry contribute to fitness, or why is it necessary? "All our limbs and organs," says Payne Knight, "serve us in pairs, and by mutual co-operation with each other: whence the habitual association of ideas has taught us to consider this uniformity as indispensable to the beauty and perfection of the animal form. There is no reason to be deduced from any abstract consideration of the nature of things, why an animal should be more ugly and disgusting for having only one eye, or one ear, than for having only one nose or one mouth; yet if we were to meet with a beast with one eye, or two noses, or two mouths, in any part of the world, we should, without inquiry, decide it to be a monster, and turn from it with abhorrence: neither is there any reason, in the nature of things, why a strict parity, or relative equality, in the correspondent limbs and features of a man or a horse, should be absolutely essential to beauty, and absolutely destructive of it in the roots and branches of a tree. But, nevertheless, the Creator having formed the one regular, and the other irregular, we habitually associate ideas of regularity to the perfection of one, and ideas of irregularity to the perfection of the other; and this habit has been so unvaried, as to have become natural."