A readable introduction to human and animal muscles: the different kinds of muscle cells and how they contract, a bit about their chemistry, and a look at how different animals get around. Basic concepts are simply explained and nothing is assumed: there are brief digressions on such physical phenomena as buoyancy, hydraulic compression and air resistance when they help to clarify the different processes of locomotion. This is an easy subject for direct observation and the Silversteins frequently suggest moving certain muscles, watching a dog walk and run, etc., thus demonstrating points being made in the text. Throughout comparisons and analogies vivify without oversimplifying: an ant can carry 50 times its weight, comparable to a man carrying three automobiles on his back -- but if an ant as big as a man could exist he probably wouldn't be much stronger. Functional, and it moves easily along.