This fastens the foot to any smooth surface. Many insects have these sticky hairs on their foot pads. When a fly walks up a window pane, it does it by gluing its feet, one after the other, to the glass. I don't wonder you laugh. No, Mollie, the glue does not harden and hold it fast. The fly can easily pull its foot loose. The grasshopper cannot walk on glass quite as well as the fly. Its foot pads do not cling so well. [Illustration] Would you not like to know the name of these curious little foot pads? We call the foot pad a _pulvillus_. Some insects do not have sticky hairs on the pulvillus. There are beetles that simply put the pulvillus so flat against a smooth surface that it stays there by the pressure of the air above. Some people think that is the way the pulvillus on the fly's foot acts. Perhaps it acts both ways, sucking fast and sticking by hairs. John wants to know if the beetle's pulvillus does not act just like the "sucker" that boys make. The sucker, you know, is a round piece of leather with a string attached to the middle. When the leather is wet and laid flat on the floor or on a smooth stone, all the air below it is pushed out, and the air above presses so hard that a boy cannot pull the leather up from the floor. [Illustration] You can peel it up from one edge and let the air under easily enough, and then a baby could lift it. When the insect wants to move, it peels its foot loose. It can do this very quickly. Mollie wants to know what all these little sharp spines on the back of the tibia are for. Let us look at them. There is a double row of them. Do they not look a little like a comb? I suspect that is what they are, the grasshopper's comb. Insects are very neat little folks. They are always cleaning their wings and their legs and their antennae and their bodies. The spines on their legs are very convenient for that. Charlie says he thinks the grasshopper's legs are as good as a whole box of tools. So they are, and you have not yet heard all they can do. The funniest is to come. Mr. Grasshopper sings his song with his hind legs! He rubs the inside of his femurs against the outside of his wings. There is a row of very fine spines down the inside of the femur for the use of the little fiddler. He scrapes away with these on his wing covers. Yes, Ned, his femur is his violin bow, and his wing cover is his violin. The noise he makes does not sound much like a violin, little Nell thinks. No, indeed, it does not. It is the shrilling sound we hear in the grass in the summer time. [Illustration] It is only the male grasshopper that sings. The little lady grasshopper sits still and listens to him. Now, let us look at the other legs. The front pair are the smallest. Can you find the little coxa and trochanter? Yes, Charlie, we will draw the little front leg. Let us number the segments as we did those of the hind leg.