That's what mean people used to call their bespectacled chums back before geeks and nerds took over the world. I doubt they'd say that if they came across a guy who really, ACTUALLY had four eyes. They'd probably say something like "look at that guy! He has four eyes!" And all his friends would think he meant someone was wearing glasses and they'd wonder what all the fuss was about.
But what about a fish with four eyes?
And I can say that because the Four-eyed Fish doesn't really, ACTUALLY have four eyes. It just looks like it does. And acts like it does. And kind of... sees the world as if it does. Nice trick if you can pull it off!
What we're looking at here is a genus of three fish found in Central and South America. They spend their time swimming about at the surface of rivers and sometimes even out in coastal sea water. And when I say "the surface", I really mean it. ACTUALLY!
So, an extra pair of eyes on the top of your head would be great. Probably not possible, but great. And when things are great but not possible, it may be time to compromise. So the Four-eyed Fish doesn't have four eyes, it has two eyes, each one divided in two.
Each eye has one lens. So far, so normal. Each eye also has two pupils and two retinas. No longer normal.
One pupil faces upward, the other downward. The lens is also thicker in the lower half than the upper, so while there is only one lens, it's adapted to provide good sight in both water and air at the same time. They're bifocals!
Now old Four-eyes can cruise the water with confidence, snatching insects that fall on the river, chomping on other small fish and swimming away before the eagles can strike!
With all that effort to survive, it's time to lay some eggs. Except that the Four-eyed Fish doesn't lay eggs, they're livebearers. They're even in the order Cyprinodontiformes, which is the one that contains all those aquarium fish like guppies, platies and mollies - the ones where once you have one male and one female, it takes a protracted effort to not have 50. It's a little more complicated for Four-eyes, though...
|Image: A. Jaszlics|
It means that instead of half the population mating with the other half, you have a quarter mating with another quarter. It's not clear how this can be a good thing, but perhaps the Four-eyed Fish just really enjoys dividing things in two.