The chief parts to notice in a fly’s head are its eyes. These are so large that they make up nearly all the head. These big bright eyes look as if they had varnish on them. Now each of these eyes is made up of a very great many small eyes. There are four thousand of these small eyes. [Illustration] Between these two big eyes are three little single eyes, set in this way-- Wise men have studied the eyes of flies for many years, and do not yet know all about them. The wings of a fly have a fine, thin, clear covering. This is held out on a tiny frame, like a net-work. The fly moves these wings very quickly. The motion of the wings helps to make the sound or _buzz_ of the fly. Now we come to the legs and feet of our fly. The leg is made in five joints. The foot also has five joints. The last joint of the foot has two claws and a little pad. These are covered with fine hairs. The hairs catch on little points or rough edges. Thus the fly can walk, as you would say, “upside down,” and does not fall. Besides, the pad and hairs act like a sucker. They suck air from under the foot. So they hold the fly from falling as he runs up a pane of glass. All boys know what a “sucker” is and how to make one. LESSON XVIII. MRS. FLY AND HER FOES. I suppose you have heard your mother wish there were not so many flies. The fact is, flies make us much trouble. Their noise tires and vexes people. They lay eggs in and on the food, and so spoil it. They cover our clean walls and glass with small black spots. Will you wonder that there are so many flies when I tell you that one fly can in one season be the mother of two million others! Many insects die soon after laying eggs. Bees and wasps do not, nor do flies. Bees and wasps take care of their eggs and their young, but the fly mother does not. Mrs. Fly has more than a hundred eggs to lay at once. It is quite plain she could not take care of so many babies. She must let them all look out for themselves. Still Mrs. Fly shows much sense as to where she puts her eggs. She finds a place where they will be likely to live and get food and grow. If the place is too wet the baby flies would drown when they leave the egg. If the place is too dry, they would wither up and die. Then, too, they must have soft food. [Illustration: A Tavern by the Way.] The fly does not lay her eggs on a stone or a piece of wood. She lays them in some kind of food. The fly can live all summer if it has a fair chance. Cold kills flies. A frosty day will kill them. Some few flies, like a few of the wasps, hide, and live over winter in a torpid state, and in the spring they come out to rear new swarms. Birds, spiders, wasps, cats, dogs, and some other animals eat flies. These creatures kill flies by millions. People kill flies with poison and fly-traps. If so many were not killed, we should be overrun with them.