This well-researched biography of a forgotten scientist also suggests a revealing view of 19th-century American science. Warren, a professor at the Wistar Institute of Anatomy and Biology in Philadelphia, gives an account of the man who was once considered the most distinguished American biologist of his time, while also exploring some reasons for his present-day obscurity. Like Darwin, a contemporary, Leidy the boy was a passionate observer and collector of natural specimens. Forced by his parents to study medicine, he practiced only briefly in Philadelphia before his descriptions and drawings of mollusks brought him recognition from the leading scientific societies in the country. When he was 23, the Academy of Natural Sciences of Philadelphia named him its librarian and, soon after, chairman of its board of curators. He also became curator of the Anatomical Museum at the University of Pennsylvania and professor of anatomy, as well as chair of the anatomy department there. Although he taught anatomy and wrote a basic textbook on the subject, his love was natural history--protozoology, parasitology, paleontology, entomology. As his reputation grew, field collectors sent him specimens from around the country to identify. He duly studied them, producing a remarkable mass of data on tens of thousands of organisms. However, the era of descriptive science, Leidy's domain, was already ending, replaced by a new age of experimental science. Consequently, his work, though impressive, began to seem outmoded. Unlike Darwin, the conservative Philadelphian avoided controversy and did not theorize; no grand synthesis emerged from his work. A sympathetic portrait of a talented, diligent man who laid a foundation for others, but lacked the imagination to build a memorable monument.