The most efficient muscle-fibres in the animal kingdom are found in insects. This will not surprise anyone who thinks of an insect’s power of movement. If a man could jump as many times his own height as a flea can, he would clear the dome of St. Paul’s. An ant can drag an object sixty times as heavy as itself, with no wheels beneath it to diminish friction. Under the same conditions a horse cannot drag much more than its own weight. A dragon-fly, it is asserted—although we have not met a man who guarantees that he has made the observation—will support its heavy body in the air by the rapid vibration of its wings for four-and-twenty hours without alighting. The chirp of a cricket is produced by the rubbing together of its hind-legs. A mosquito sounds its war-cry much in the same way. The pitch of the note proves that the insect’s muscles are contracting and relaxing at least 300 times a second. None of these figures must be applied without qualifications in estimating the relative strength of insect and human muscle. Weight for weight, the muscle of a flea is not so much stronger than ours as the figures might lead one to infer. To ascertain the numerical relation, it is necessary to compare the total cross-section of the two chief segments of a flea’s leg with the cross-section of the extensor muscles of a man’s thigh and calf, and a man’s weight with the weight of a flea. Nevertheless, after all deductions have been made, a considerable balance of superiority lies with the insect as regards the strength of its muscles, their rapidity of contraction, and power of repeating contraction without fatigue. An insect’s muscle is the most suitable that can be obtained for microscopic examination. Its pattern is larger and more distinct than that of other animals. That the pattern should be larger is not quite what might have been expected. It would not have surprised us had we found the pattern finer in the more effective type. Nothing is easier than to mount a specimen of insect-muscle. The large water-beetle (_Dytiscus marginalis_) is an excellent subject. It is so easily handled. Having cut off the animal’s head, a leg is pulled out from the thorax. It is split open with a penknife, and a little of the muscle is dug out from within its hard case, placed on a clean slide, and covered with a cover-slip. If the preparation has been made quickly and cleanly, the muscle remains alive for five or ten minutes. Not only can it be studied, with the microscope, unaltered by reagents, but under the most favourable circumstances the progress along its fibres of waves of contraction can be watched. The structure of the fibres is more easily made out if a little salt-solution or white of egg is added to the preparation. [Illustration: FIG. 16.—A, A MINUTE PORTION OF AN INSECT’S MUSCLE-FIBRE, HIGHLY MAGNIFIED. B, WHITE FIBRE OF MAMMALIAN MUSCLE.