The “eyes” of the terricola are black dots arranged in two parallel rows along both sides of the back. Some species are two-eyed. Many varieties are eyeless. Hundred-eyed worms are quite common. The black dots are light-sensitive. Presumably they represent the beginning of vision. By means of them the worms can distinguish between light and darkness. They also tell the direction from which light comes. Actually, however, planarians without eyes have the same ability, but they are slower to react. This is demonstrably true for fresh-water forms. For most of the land forms at least exposure to strong sunlight would be fatal. Each of the eye dots has a nerve connection with the brain. It is quite unlikely, however, that the animals actually see anything, in the sense of discriminating specific objects in their surroundings. In a few species, however, from two to four of these black dots nearest to the brain seem somewhat more complicated than the others. As the faculty of vision evolves among animals these will become actual eyes and all the other light-sensitive spots will be discarded. In most planarians, however, the number of eyes increases with the age of the animal. Nearly all are predatory meat eaters. They are both hunters and scavengers. Some pursue, kill, and eat living animals, such as earthworms and small mollusks, as big as themselves. They apparently are able to locate their victims at some distances by an already evolved sense of smell. One blind Brazilian species is said to pursue earthworms into their burrows several feet underground. When the victim is overtaken the planarian first enfolds it in its sheetlike, slimy body. Then from its mouth, always on the underside of the body near the middle instead of at the head end, it projects its pharynx, a muscular tube which is part of the digestive system. From this is exuded a substance of some sort which slowly liquifies the flesh. Then the liquid is sucked into the body through the mouth. Digestion then is completed within the digestive tract by special cells which engulf minute particles in the same way as they are engulfed and digested by one-celled animals, the amoeba. The nature of the dissolving material exuded from the pharynx is unknown. It is believed, however, to contain a mixture of enzymes such as those found in the intestinal tracts of higher animals.