Specialization of the Skeleton.--Homologies of Bones of Fishes.--Parts of the Skeleton.--Names of Bones of Fishes.--Bones of the Cranium.--Bones of the Jaws.--The Suspensorium of the Mandible.--Membrane Bones of Head.--Branchial Bones.--The Gill-arches.--The Pharyngeals.--The Vertebral Column.--The Interneurals and Interhæmals.--The Pectoral Limb.--The Shoulder-girdle.--The Posterior Limb.--Degeneration.--The Skeleton in Primitive Fishes.--The Skeleton of Sharks.--The Archipterygium. 34 CHAPTER V. MORPHOLOGY OF THE FINS OF FISHES. Origin of the Fins of Fishes.--Origin of the Paired Fins.--Development of the Paired Fins in the Embryo.--Evidences of Palæontology.--Current Theories as to Origin of Paired Fin.--Balfour's Theory of the Lateral Fold.--Objections.--Objections to Gegenbaur's Theory.--Kerr's Theory of Modified External Gills.--Uncertain Conclusions.--Forms of the Tail in Fishes.--Homologies of the Pectoral Limb.--The Girdle in Fishes other than Dipnoans. 62 CHAPTER VI. THE ORGANS OF RESPIRATION. How Fishes Breathe.--The Gill Structures.--The Air-bladder.--Origin of the Air-bladder.--The Origin of Lungs.--The Heart of the Fish.--The Flow of Blood. 91 CHAPTER VII. THE NERVOUS SYSTEM. The Nervous System.--The Brain of the Fish.--The Pineal Organ.--The Brain of Primitive Fishes.--The Spinal Cord.--The Nerves. 109 CHAPTER VIII. THE ORGANS OF SENSE. The Organs of Smell.--The Organs of Sight.--The Organs of Hearing.--Voices of Fishes.--The Sense of Taste.--The Sense of Touch. 115 CHAPTER IX. THE ORGANS OF REPRODUCTION. The Germ-cells.--The Eggs of Fishes.--Protection of the Eggs.--Sexual Modification. 124 CHAPTER X. THE EMBRYOLOGY AND GROWTH OF FISHES. Post-embryonic Development.--General Laws of Development.--The Significance of Facts of Development.--The Development of the Bony Fishes.--The Larval Development of Fishes.--Peculiar Larval Forms.--The Development of Flounders.--Hybridism.--The Age of Fishes.--Tenacity of Life.--Effect of Temperature on Fishes.--Transportation of Fishes.--Reproduction of Lost Parts.--Monstrosities among Fishes. 131 CHAPTER XI. INSTINCTS, HABITS, AND ADAPTATIONS. The Habits of Fishes.--Irritability of Animals.--Nerve-cells and Fibers.--The Brain or Sensorium.--Reflex Action.--Instinct.--Classification of Instincts.--Variability of Instincts.--Adaptations to Environment.--Flight of Fishes.--Quiescent Fishes.--Migratory Fishes.--Anadromous Fishes.--Pugnacity of Fishes.--Fear and Anger in Fishes.--Calling the Fishes.--Sounds of Fishes.--Lurking Fishes.--The Unsymmetrical Eyes of the Flounder.--Carrying Eggs in the Mouth. 152 CHAPTER XII.