. Beginners' Zoology . gth of the joints of the leg the same in P^^, beetles, etc., as in the wasp (Figs.)? Figure 125 isa diagram of an insects leg cut lengthwise. The leg consists ofthick-walled tubes (<?, n) with their ends held together by thin,easy-wrinkling membranes which serve as joints. Thus motion isprovided for at the expense of strength. When handling liveinsects they should never be held by the legs, as the legs comeoff very easily. Does the joint motion of insects most resemblethe motion of hinge joints or ball-and-socket joints? Answer bytests of living insects.
. Beginners' Zoology . gth of the joints of the leg the same in P^^, beetles, etc., as in the wasp (Figs.)? Figure 125 isa diagram of an insects leg cut lengthwise. The leg consists ofthick-walled tubes (<?, n) with their ends held together by thin,easy-wrinkling membranes which serve as joints. Thus motion isprovided for at the expense of strength. When handling liveinsects they should never be held by the legs, as the legs comeoff very easily. Does the joint motion of insects most resemblethe motion of hinge joints or ball-and-socket joints? Answer bytests of living insects. There are no muscles in the foot of aninsect. The claw is moved by a muscle (;«) in the thigh with whichit is connected by the long tendon (2, s, t, v). In which part arethe breathing muscles? As the wings are developed from foldsof the dorsal skin, the wing has two layers, an upper and a lowerlayer. These inclose the so-called nerves or ribs of the wing,each of which consists of a blood tube inclosed in an air 76 BEGINNERS ZOOLOGY The abdomen in various species consists of from five^to eleven overlapping rings with their foldlike joints be-tween them. Does each ring overlap the ring in frontor the one behind it ? The food tube (Fig. 127) begins at the mouth, whichusually bears salivary glands (4, Fig. 127, which repre-sents internal organs of the grasshopper). The food tubeexpands first into a croplike enlargement; next to thisis an organ (6, Fig. 127), which resembles the gizzard
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