"Why, I think there can be no doubt what it is for. When the city has been growing for some time, some of the nurseries will be very high up above the queen's house; but the labourers have to carry her eggs into them, no matter how far off they may be. If they carry them through all the streets, they will have to walk as many as fifteen or twenty feet, for it would be five or six feet in a perfectly straight line, and these streets are very crooked; but if they make a bridge in the open space in the centre, they can then go from the queen's house over the bridge, and get to the upper nurseries without travelling more than two feet. So they made the bridge to shorten the way, to be sure." "This is very wonderful: but you said something about large trenches or gutters underground; what are they, Uncle Philip?" "These galleries lead from the city under ground, and are as large as the bore of a large cannon; they are thirteen inches across, and more than a hundred yards long. I have already told you that the labourers never come out into the light, when they can help it; and these underground ways are the great roads to the city, to fetch in clay, or wood, or water, or provisions: and now I will tell you another thing which shows a great deal of sense. As some of their houses are very high up, you know they would find it very hard to climb up through all the streets with a heavy load in a straight line; so when these large ways underground reach the outside wall, they just come through and keep on winding around the inside of it like a corkscrew all the way to the top; and there are other galleries opening from it at different places into the city. One thing has been noticed about these ants; they can scarcely climb at all up a perpendicular wall. Therefore on the upright side of any part of the city you may see a road made, standing out from the wall like a ledge; it is flat on the top, and half an inch wide, and goes up gradually like a stair-case, or like a road cut out on the side of a mountain. "Here is a picture of one of their cities cut straight down through the middle. At the bottom, in the centre, is the queen's house; over it is a floor, and the two crooked things you see rising up from the floor, are bridges." [Illustration] "But, Uncle Philip, you said you would tell us about the soldiers and labourers coming out when the city is attacked."