A very good, well-written popular survey of representative egg-laying vertebrates as developmental phenomena on the evolutionary scale, with emphasis on methods of reproduction. The author, a scientific journalist, has his sights on adaptive movement and change through the millennia -- from the notochordal (forerunner of the spinal column) sea lancet up through the nesting bird, and he thoughtfully provides the novice with a chapter on classification, as an aid to an orderly view of the phylum Chordata. The amphibians receive, not surprisingly, a great deal of attention since they evolved the ""basic body plan of land-dwelling vertebrates"" -- a four-limbed body, spine, limb girdles, etc. But it was the reptilian egg that ""made possible the conquest of the land by reptiles, birds and then mammals,"" and Stivens discusses some ""living fossils"" and others of more modem derivation. The largest section of the book concerns birds -- of reptilian ancestry but warm-blooded and able to develop a high metabolism. Evolution unscrambled.