Queer Kinds of Eyes,

New Zealand Graphic, Volume XXXIII, Issue XVII, 22 October 1904, Page 60

Queer Kinds of Eyes,

Look at the next spider you find, and try to find the eight shiny little eyes at the anterior end, some above and some put under the edge of what we may imagine to be its forehead. To examine these parts t'o best advantage hold the spider in tweezers, or it may be better to use a spider killed by being dropped into a bottle of diluted alcohol. These eight eyes vary in arrangement and in relative size in various species of spiders—in some they may be arranged in two rows, in others in three; some may be very small and others large and prominent; and so on—-but there they are; rather poor eyes, near-sight-ed. looking in several directions at once, and the spider, who can never shut any of them, is sure to see everything that approaches, unless she is asleep, in which case the sight is dead. For some purposes it may be convenient to have eyes that roll up and disappear at the approach of danger. And these are exactly what the snail has, situated at the end ot two long and sensitive palpi, or feelers. When all is quiet their owner extends these organs, and you can see at their tips small round knobs upon which the eyes are placed. But if you touch one of the palpi, or even jar the snail a little, the eyes begin to back into these feelers as the tip of a glove finger may be turned in, and they no longer see any danger that may be lurking at hand.

Queer animal that, which dares t® peep at the world only when it is in perfect safety, and refuses to look whea danger threatens! But the snail never had much reputation for bravery, and therefore has little to lose.

But there are many animals whose eyes are not perfect enough to form a complete image, or even parts of an image, but which can receive only a sensation of light and perhaps, in some cases, an indistinct impression of colour and among those that can in this way perceive light, it is probable that the sensation is more like what we call heat than it is like actual vision. In the simplest of these eyes, the “eye” consists of nothing more than a little mass of, dark colouring matter, known as pigment, placed around the outer edge of a nerve. You know how much warmer on a! hot day a black dress is than a white one, and a black sunshade seems to collect more heat than does a light one. In a similar way the little black mass of pigment absorbs the heat in the strong light, and by this simple means the animal may be liable to perceive the direction of the light and regulate its action accordingly. A greatly-improved form of this pig-ment-eye is seen in a tiny crustacean, that is, a crab-like animal, about the size of a pin-head, and found almost everywhere in fresh-water ponds and ditches. Its name is Daphiua.