Even a cursory study of such texts as Dana's _"Manual of Geology"_ will reveal that the development of the plants and animals through the "ages" of speculative geology does not move forward like a steadily rising flood. There is rather a series of great waves, each rising abruptly, new forms often appearing suddenly and together. The very simplest known fossils, the trilobites, of which nearly a hundred species are known in America alone, and certain cephalopods (sea snails) are animals highly complex in structure and regarded by Le Conte as "hardly lower than the middle of the animal scale." The trilobites possess well developed compound eyes and the cephalopods have simple eyes, almost as complex as the eyes of man, possess a well defined stomach, a systemic heart, a liver, and a highly developed nervous system [tr. note: no period in original] Observe, that these two highly organized forms of animals, "hardly to be regarded as lower than the middle of the animal scale," are the very "oldest" animals found in fossil form! In other words, of at least one half of the total progress of the animal kingdom every vestige is lost. If we turn a few pages in Dana's _"Manual"_ we find in the sandstone of the "Devonian Era" gigantic species of fish. The entire record of evolution from the mollusk to the fish is lost! There is not a single transitional form. These fishes have organs as complex and perfect as the fishes of to-day. Suddenly, in the "carbonic age" amphibia and reptiles appear, and then come, in the "Triassic" the huge reptiles known as dinosaurs. Insects and scorpions have been found in the "Silurian." [tr. note: sic on punctuation] They stand among the highest of even _living_ articulates, and they are the "oldest" known airbreathing animals. "We seek in vain for the progenitors of these highly organized articulates or for some conceivable method by which their wings and special breathing apparatus could have evolved. We do not know that these first insects and scorpions have made any material progress through all the ages." (Fairhurst.)