Hundreds of species of marine life manage to survive even in the darkest depths of the ocean. These tenants of the deep have evolved some extremely ingenious devices for locating their food and enemies. Where the light is very dim, some of these species have developed enormous eyes with almost telescopic lenses, very much like those of owls. Others, especially the fish that survive where there is no light at all, are quite blind but have developed long feelers that enable them to identify and collect stray bits of food that come within a considerable radius of them. Some inhabitants of the deep supply their own light. They have built-in torches that they can switch on and off depending on whether they are pursuing of being pursued. Some have regular lamps, spots of steady light, which spread a faint glow through the water around them. One deepwater squid can squirt a luminous fluid that lights up its immediate vicinity, a neat variation on the ink ejected by its cousins nearer the surface to becloud and darken water. It is supposed that about half of the varieties of fish living in the dark depths of the ocean have some power of illumination. Most of the marine species living in the darkest depths have ______.