Note 39 — PART I.—MORPHOLOGY AND PHYSIOLOGY (continued 5)

It has been suggested to us by A. A. Packard that the power possessed by insects of transporting loads much heavier than themselves is easily accounted for, when we consider that the muscles of the legs of an insect the size of a house-fly (¼ inch long), and supporting a load 399 times its own weight, would be subjected to the same stress (per square inch of cross-section) as they would be in a fly 100 inches long of precisely similar shape, that carried only its own weight; from the mechanical law that, while the weight of similar bodies varies as the cube of the corresponding dimensions, the area of cross-section of any part (such as a section of the muscles of the leg) varies only as the square of the corresponding dimensions. In short, the muscles of a fly carrying this great proportional weight undergo no greater tension than would be exerted by a colossal insect in walking.