David Starr Jordan's authoritative work undertakes a rigorous examination of fish taxonomy, mapping the transition from ancient, primitive lineages to modern teleosts. The treatise begins by exploring the ganoids, evaluating their cartilaginous skeletons, enameled plates, and spiral intestinal valves, while weighing whether they constitute a true natural group. Jordan investigates the anatomical characteristics that link these archaic forms to modern bony fishes, debating the classifications proposed by contemporary ichthyologists such as Johannes Müller and Theodore Gill.
Moving systematically through the suborder Isospondyli, the author analyzes the anatomical features of herring-like and trout-like fishes, emphasizing the presence of the mesocoracoid arch and the general absence of fin spines. The discussion covers marine and freshwater families, tracking their distribution, habits, and developmental stages, including the curious larval forms of eels and the metamorphosis of the lady-fish. Each group is subjected to careful osteological scrutiny to determine its place in the genealogical tree.
The volume pays particular attention to the Salmonidæ, providing detailed accounts of the Pacific salmon, whitefish, grayling, and various trout species. Jordan evaluates the life cycle of anadromous fishes, their spawning migrations, and the physiological changes that accompany sexual maturity. He examines the ongoing debates regarding the parent-stream theory and details the practical methods of artificial propagation and commercial packing.
Throughout the text, Jordan addresses the complexities of nomenclature and classification, acknowledging the difficulties of arranging fish into a linear series. He weighs the value of internal and external diagnostic characters, such as the structure of the vomer, the number of pyloric caeca, and the arrangement of the pharyngeal teeth in cyprinids. The narrative extends through specialized marine orders, deep-sea lantern-fishes, and degenerate apodal forms, concluding with a thorough review of the catfishes and their characteristic Weberian apparatus.
Jordan avoids broad generalizations, grounding every conclusion in concrete anatomical detail and the observed facts of distribution and embryology. The text remains a monument of classical ichthyology, reflecting the state of scientific knowledge at the turn of the twentieth century. While modern taxonomy has refined many of the relationships discussed, Jordan's systematic approach and rigorous documentation provide an enduring foundation for the study of aquatic life.
