Muscles And Locomotion

FIGURE 14.5. (A) Musculature of coxa; (B) segmental musculature of leg; and (C) musculature of hindleg of grasshopper. [A, C, from R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company. B, reproduced by permission of the Smithsonian Institution Press from Smithsonian Miscellaneous Collections, Volume 80, Morphology and mechanism of the insect thorax, Number 1, June 25, 1927, 108 pages, by R. E. Snodgrass: Figure 39, page 89. Washington, D.C., 1928, Smithsonian Institution.]

FIGURE 14.5. (A) Musculature of coxa; (B) segmental musculature of leg; and (C) musculature of hindleg of grasshopper. [A, C, from R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company. B, reproduced by permission of the Smithsonian Institution Press from Smithsonian Miscellaneous Collections, Volume 80, Morphology and mechanism of the insect thorax, Number 1, June 25, 1927, 108 pages, by R. E. Snodgrass: Figure 39, page 89. Washington, D.C., 1928, Smithsonian Institution.]

of the coxa; contraction of the coxal promotor causes the coxa to twist forward, thereby effecting protraction (a forward swing) of the entire leg; (2) the coxal adductor and abductor (attached to the sternum and pleuron, respectively), which move the coxa toward or away from the body; (3) anterior and posterior coxal rotators, which arise on the sternum and assist in raising and moving the leg forward or backward; and (4) an extensor (levator) and flexor (depressor) muscle in each leg segment, which serve to increase and decrease, respectively, the angle between adjacent segments. It should be noted that the muscles that move a particular leg segment are actually located in the next more proximal segment. For example, the tibial extensor and flexor muscles, which alter the angle between the femur and tibia, are located within the femur and are attached by short tendons inserted at the head of the tibia.

It is the coordinated actions of the extrinsic and intrinsic muscles that move a leg and propel an insect forward. In considering how propulsion is achieved, it must also be remembered that another important function of a leg is to support the body, that is, to keep

FIGURE 14.6. Magnitude of the longitudinal and lateral forces resulting from the strut effect for each leg in its extreme position. [After G. M. Hughes, 1952, The coordination of insect movements. I. The walking movements of insects, J. Exp. Biol. 29:267-284. By permission of Cambridge University Press, London.]

FIGURE 14.6. Magnitude of the longitudinal and lateral forces resulting from the strut effect for each leg in its extreme position. [After G. M. Hughes, 1952, The coordination of insect movements. I. The walking movements of insects, J. Exp. Biol. 29:267-284. By permission of Cambridge University Press, London.]

it off the ground. In the latter situation, a leg may be considered as a single-segmented structure—a rigid strut. If the strut is vertical, the force along its length (axial force) will be solely supporting and will have no propulsive component. If the strut is inclined, the axial force can be resolved into two components, a vertical supportive force and a horizontal propulsive force. Because the leg protrudes laterally from the body, the horizontal force can be further resolved into a transverse force pushing the insect sideways and a longitudinal force that causes backward or forward motion. The relative sizes of these horizontal forces depend on (1) which leg is being considered and (2) the position of that leg. Figure 14.6 indicates the size of these forces for each leg at its two extreme positions. It will be apparent that in almost all of its positions the foreleg will inhibit forward movement, whereas the mid- and hindlegs always promote forward movement. In equilibrium, that is, when an insect is standing still, the forces will be equal and opposite. Movement of an insect's body will occur only if the center of gravity of the body falls. This occurs when the forces become imbalanced, for example, by changing the position of a foreleg so that its retarding effect is no longer equal to the promoting effect of the other legs, whereupon the insect topples forward (Hughes and Mill, 1974).

Also important from the point of view of locomotion is the leg's ability to function as a lever, that is, a solid bar that rotates about a fulcrum and on which work can be done. The fulcrum is the coxothoracic joint and the work is done by the large, extrinsic muscles.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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