Below the forehead are the eyes, which form the most precious portion of the human body, and which, by the enjoyment of the blessings of sight, distinguish life from death. Eyes, however, have not been granted to all animals; oysters have none, but, with reference to some of the shell-fish, the question is still doubtful; for if we move the fingers before a scallop half open, it will immediately close its shell, apparently from seeing them, while the solen[1] will start away from an iron instrument when placed near it. Among quadrupeds the mole[2] has no sight, though it has something that bears a resemblance to eyes, if we remove the membrane that is extended in front of them. Among birds also, it is said that a species of heron, which is known as the "leucus,"[3] is wanting of one eye: a bird of most excellent augury, when it flies towards the south or north, for it is said that it portends thereby that there is about to be an end of perils and alarms. Nigidius says also, that neither locusts nor grasshoppers have eyes. In snails,[4] the two small horns with which they feel their way, perform the duties of eyes. Neither the mawworm[5] nor any other kind of worm has eyes.