The provided text is an excerpt from a comprehensive textbook on the biology of amphibians, authored by G. K. Noble and published by McGraw-Hill in 1931. The book aims to summarize the relationships and biology of amphibians, including frogs and salamanders, and is intended for both students and field naturalists. The content is divided into two main parts: "Their Structure and Functions" and "Relationships and Classification." In the first part, Noble discusses the origin of amphibians, their development, heredity, and various physiological and anatomical aspects. He explains how amphibians evolved from fish-like ancestors, detailing the changes in their skeletal, respiratory, circulatory, digestive, muscular, and other systems. The text also covers the modes of life, speciation, adaptation, and the role of sex and secondary sexual characters in amphibians. The second part focuses on the classification and relationships of amphibians, listing and describing various orders such as Labyrinthodontia, Phyllospondyli, Lepospondyli, Gymnophiona, Caudata, and Salientia. Noble provides detailed comparisons and illustrations to help readers understand the evolutionary transitions and structural differences among these groups. The book is a valuable resource for understanding the biology and evolution of amphibians, providing a comprehensive overview of their anatomy, physiology, and ecological roles.The provided text is an excerpt from a comprehensive textbook on the biology of amphibians, authored by G. K. Noble and published by McGraw-Hill in 1931. The book aims to summarize the relationships and biology of amphibians, including frogs and salamanders, and is intended for both students and field naturalists. The content is divided into two main parts: "Their Structure and Functions" and "Relationships and Classification." In the first part, Noble discusses the origin of amphibians, their development, heredity, and various physiological and anatomical aspects. He explains how amphibians evolved from fish-like ancestors, detailing the changes in their skeletal, respiratory, circulatory, digestive, muscular, and other systems. The text also covers the modes of life, speciation, adaptation, and the role of sex and secondary sexual characters in amphibians. The second part focuses on the classification and relationships of amphibians, listing and describing various orders such as Labyrinthodontia, Phyllospondyli, Lepospondyli, Gymnophiona, Caudata, and Salientia. Noble provides detailed comparisons and illustrations to help readers understand the evolutionary transitions and structural differences among these groups. The book is a valuable resource for understanding the biology and evolution of amphibians, providing a comprehensive overview of their anatomy, physiology, and ecological roles.