The leg of an insect (Fig. 125) has five joints (two short joints, two long, and the foot). Named in order from above, they are (1) the hip (coxa), (2) thigh ring (trochanter), (3) thigh (femur), (4) the shin (tibia), (5) the foot, which has five parts. Which of the five joints of a wasp’s leg (Fig. 161) is thickest? Slenderest? Shortest? One joint (which?) of the foot (Fig. 161) is about as long as the other four joints of the foot combined. Is the relative length of the joints of the leg the same in grasshoppers, beetles, etc., as in the wasp (Figs.)? Figure 125 is a diagram of an insect’s leg cut lengthwise. The leg consists of thick-walled tubes (_o_, _n_) with their ends held together by thin, easy-wrinkling membranes which serve as joints. Thus motion is provided for at the expense of strength. When handling live insects they should never be held by the legs, as the legs come off very easily. Does the joint motion of insects most resemble the motion of hinge joints or ball-and-socket joints? Answer by tests of living insects. There are no muscles in the foot of an insect. The claw is moved by a muscle (_m_) in the thigh with which it is connected by the long tendon (_z_, _s_, _t_, _v_). In which part are the breathing muscles? As the wings are developed from folds of the dorsal skin, the wing has two layers, an upper and a lower layer. These inclose the so-called “nerves” or ribs of the wing, each of which consists of a blood tube inclosed in an air tube. The =abdomen= in various species consists of from five to eleven overlapping rings with their fold-like joints between them. Does each ring overlap the ring in front or the one behind it? [Illustration: FIG. 127.—VISCERA OF GRASSHOPPER. Key in text. Compare with Fig. 114. ] [Illustration: FIG. 128.—AIR TUBES OF INSECT. ] The =food tube= (Fig. 127) begins at the mouth, which usually bears salivary glands (4, Fig. 127, which represents internal organs of the grasshopper). The food tube expands first into a _croplike_ enlargement; next to this is an organ (6, Fig. 127), which resembles the gizzard in birds, as its inner wall is furnished with chitinous teeth (_b_, Fig. 114). These reduce the food fragments that were imperfectly broken up by the biting jaws before swallowing. _Glands_ comparable to the liver of higher animals open into the food tube where the stomach joins the small intestine. At the junction of the small and the large intestine (9) are a number of _fine tubes_ (8) which correspond to _kidneys_ and empty their secretion into the large intestine.