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[191] will start away from an iron instrument when placed near it. Among quadrupeds the mole[192] 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,”[193] 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,[194] the two small horns with which they feel their way, perform the duties of eyes. Neither the mawworm[195] nor any other kind of worm has eyes. CHAP. 53.—THE DIVERSITY OF THE COLOUR OF THE EYES. The eyes vary in colour in the human race only; in all other animals they are of one uniform colour peculiar to the kind, though there are some horses that have eyes of an azure colour. But in man the varieties and diversities are most numerous; the eyes being either large, of middling size, remarkably small, or remarkably prominent. These last are generally supposed to be very weak, while those which are deep-seated are considered the best, as is the case also with those which in colour resemble the eyes of the goat. CHAP. 54.—THE THEORY OF SIGHT—PERSONS WHO CAN SEE BY NIGHT. In addition to this, there are some persons who can see to a very great distance, while there are others, again, who can only distinguish objects when brought quite close to them. The vision of many stands in need of the rays of the sun; such persons cannot see on a cloudy day, nor yet after the sun has set. Others, again, have bad sight in the day-time, but a sight superior to that of others by night. Of persons having double pupils, or the evil eye, we have already spoken[196] at sufficient length. Blue[197] eyes are the best for seeing in the dark.