Why the Monotremata are formed into a Sub-order--The lowest of the Mammalian Class--THE PORCUPINE OR LONG-SPINED ECHIDNA--An Ant-eater, but not an Edentate--Its Correct Name--Description of the Animal--Habits and Disposition--Manner of Using the Tongue--Where it is Found--Anatomical Features: Skull, Brain, Marsupial Bones--The Young--Species of Van Diemen’s Land and New Guinea--THE WATER-MOLE, OR DUCK-BILLED PLATYPUS--The most Bird-like Mammal--Various Names--Description--Their Appearance and Movements in Water--Their Burrows--Habits of an Individual kept in Confinement--Used by Natives as Food--How they are Captured--The Young--A Family in Captivity--The Snout--Jaws--Teeth--Tongue--Fore and Hind Feet--Heel--Spur--The Shoulder Girdle--Breastbone--Concluding Remarks on the Sub-orders--Postscript 227 THE CLASS AVES.--THE BIRDS. CHAPTER I. INTRODUCTION--WING STRUCTURE AND FEATHERS--DISTRIBUTION. Introduction--Distinctive Characters of the Class Aves--Power of Flight--The Wing--Its Structure--The Six Zoo-geographical Regions of the Earth--Birds peculiar to these Regions 235 CHAPTER II. THE ANATOMY OF A BIRD. The Three Divisions of the Class Aves--ANATOMY OF A BIRD--The Skeleton--Distinctive Features--Peculiar Bone Character--The Skull--Difference between the Skull of Birds and that of Mammals--The Jawbones--Vertebral Column--Sternum--Fore-limbs--Hind-limbs--Toes--The Muscular System--How a Bird remains Fixed when Asleep--The Oil-gland--The Nervous System--The Brain--The Eye--The Ear--The Digestive System--The Dental papillæ--The Beak--Tongue--Gullet--Crop--Stomach--Uses of the Gizzard--Intestine--The Liver, Pancreas, and Spleen--The Blood and Circulatory System--Temperature of Blood of a Bird--Blood Corpuscles--The Heart--The Respiratory System--Lungs--Air-sacs--The Organs of Voice--The Egg--Classification of the Class Aves 239 CHAPTER III. DIVISION I.--THE CARINATE BIRDS (CARINATÆ). THE ACCIPITRINE ORDER--BIRDS OF PREY. VULTURES AND CARACARAS.