1 Introduction.- 1.1 Functional Anatomy and the Evolution of the Respiratory System.- 1.2 Descriptive Classification of Lung Types.- 1.2.1 Parenchymal Types.- 1.2.2 Functional Suspension of the Lung Within the Body Cavity and of the Partitions Within the Lung.- 1.2.3 Histological Structure.- 2 Morphometry of Reptilian Lungs, with Special Emphasis on the Comparison of the Unicameral Lungs of the Teju, Tupinambis nigropunctatus Spix, and the Multicameral Lungs of the Savanna Monitor, Varanus exan- thematicus (Bosc).- 2.1 Animals.- 2.2 Symbols and Definitions.- 2.3 Morphometric Methods.- 2.3.1 Techniques.- 2.3.1.1 Preparation of Tissue.- 2.3.1.2 Morphometry of Major Parameters for Comparison of Lungs and Lung Regions.- 2.3.1.3 Application of Primary (Measured) Parameters:.- 2.3.2 Discussion of Morphometric Methods.- 2.4 Morphometric Results.- 2.4.1 Relationship Between Lung Volume and Structural Type.- 2.4.2 Volumetric Relationship of Central Lumen to Parenchyma.- 2.4.3 Parenchyma.- 2.4.3.1 Distribution Within the Lung.- 2.4.3.2 Parenchymal Volume, Surface Area, Surface- to-Volume Ratio, and Equivalent Parenchymal Thickness.- 2.4.3.3 Growth Patterns.- 2.4.3.4 Volume Relationships Within Parenchymal Tissue.- 2.4.3.5 Analysis of Parenchymal Surfaces.- 2.4.3.6 Anatomical Diffusion Factor.- Degree of Exploitation of the Lung.- 2.5 Discussion: Morphometric Comparison of Reptilian Lungs.- 2.5.1 Lung Volume.- 2.5.2 Parenchymal Volume.- 2.5.3 Surface-to-Volume Ratio in Parenchyma and Respiratory Surface Area.- 2.5.4 Harmonic Mean Thickness of the Air-Blood Tissue Barrier.- 2.5.5 Capillary Bulging.- 2.5.6 Strategy in Sequence of Anatomical Adaptations for Gas Exchange by Diffusion.- 2.5.7 Pulmonary Smooth Muscle.- 2.6 Summary.- 3 The Pump Mechanism, Its Combination with the Exchanger, and Breathing Strategy.- 3.1 Symbols and Definitions.- 3.2 The Pump.- 3.3 Breathing Strategy and the Pump.- 3.4 Interaction of the Exchanger and Pump in Breathing Strategy: the Ideal High-performance Lung.- 4 Speculations on the Evolution of the Amniote Respiratory System.- 4.1 Breathing Mechanism in the First Reptiles.- 4.2 Lung Structure in the First Reptiles.- 4.3 Hollow Bones as Indicators of Lung Structure.- 4.4 Possible Respiratory Function of the Gastralia.- 4.5 Possible Role of the Ornithischian Pelvis in Breathing.- 4.6 Broadened Ribs and Alternative Breathing Mechanisms.- 4.7 Implications for the Evolution of Lung Structure.- 5 Summary.- References.