Bees belong to a class of insects known as _Hymenoptera_, which means with membranous wings; the wings of the bee are found to be composed of beautifully fine membranes. They are four in number, and, like the legs, are joined to the thorax. The front ones are called the anterior wings, and the back ones, which you will notice are smaller, are called the posterior wings, because they are behind the others. The membranes are strengthened by a kind of framework, just as a kite is strengthened by a framework of light sticks. The ribs of the framework are called “nervures,” and, as you will see from (_a_) Plate XI., there are divisions of transparent membrane in between; these are called cells. The nervures are hollow, and like our veins, they contain blood. We have seen that the bee possesses two pairs of wings, and we may wonder why this should be so, when we know that one large pair is much more powerful for flying purposes than two small pairs. You have no doubt noticed that when a bee is at rest on a flower the wings are neatly folded over the back. Now if the bee had only one pair of large wings it would not be able to fold them so compactly--the wings would, in fact, stand out on each side of the body. We shall presently see that the bees, in the course of their duties, have to clean out the cells of the comb, and in order that they may do this it is necessary for them to be able to crawl right into the cell itself. The cells in which the young worker bees are raised are only 1/5th inch in diameter, and if the wings projected when in the folded position, the bee would not be able to enter the cell. The wings therefore have been divided, so that when folded they may lie one over the other on the bee’s back, and we find that the wings, when folded, take up only 1/6th inch of room. This leaves just sufficient space for their owner to enter a cell. You will notice that a blue-bottle fly has only one pair of large wings, for it does not need to fold them closely over its back, as it has no cells to clean. Remembering what I have told you about the greater flying power of one pair of large wings, you might imagine that the division into two pairs which we have seen to be necessary would handicap the bee in flying. The difficulty is overcome by a most ingenious device, by which the bee, when flying, is able to fasten together the wings on each side, so as to form one pair of broad wings.