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THE COLLECTION OF FISHES. How to Secure Fishes.—How to Preserve Fishes.—Value of Formalin.—Records of Fishes.—Eternal Vigilance. 429 CHAPTER XXIV. THE EVOLUTION OF FISHES. The Geological Distribution of Fishes.—The Earliest Sharks.—Devonian Fishes.—Carboniferous Fishes.—Mesozoic Fishes.—Tertiary Fishes.—Factors of Extinction.—Fossilization of a Fish.—The Earliest Fishes.—The Cyclostomes.—The Ostracophores.—The Arthrodires.—The Sharks.—Origin of the Shark.—The Chimæras.—The Dipnoans.—The Crossopterygians.—The Actinopteri.—The Bony Fishes. 435 CHAPTER XXV. THE PROTOCHORDATA. The Chordate Animals.—The Protochordates.—Other Terms Used in Classification.—The Enteropneusta.—Classification of Enteropneusta.—Family Harrimaniidæ.—Balanoglossidæ.—Low Organization of Harrimaniidæ. 460 CHAPTER XXVI. THE TUNICATES, OR ASCIDIANS. Structure of Tunicates.—Development of Tunicates.—Reproduction of Tunicates.—Habits of Tunicates.—Larvacea.—Ascidiacea.—Thaliacea.—Origin of Tunicates.—Degeneration of Tunicates. 467 CHAPTER XXVII. THE LEPTOCARDII, OR LANCELETS. The Lancelet.—Habits of Lancelets.—Species of Lancelets.—Origin of Lancelets. 482 CHAPTER XXVIII. THE CYCLOSTOMES, OR LAMPREYS. The Lampreys.—Structure of the Lamprey.—Supposed Extinct Cyclostomes.—Conodontes.—Orders of Cyclostomes.—The Hyperotreta, or Hagfishes.—The Hyperoartia, or Lampreys.—Food of Lampreys.—Metamorphosis of Lampreys.—Mischief Done by Lampreys.—Migration or "Running" of Lampreys.—Requisite Conditions for Spawning with Lampreys.—The Spawning Process with Lampreys.—What Becomes of Lampreys after Spawning? 486 CHAPTER XXIX. THE CLASS ELASMOBRANCHII, OR SHARK-LIKE FISHES. The Sharks.—Characters of Elasmobranchs.—Classification of Elasmobranchs.—Subclasses of Elasmobranchs.—The Selachii.—Hasse's Classification of Elasmobranchs.—Other Classifications of Elasmobranchs.—Primitive Sharks.—Order Pleuropterygii.—Order Acanthodii.—Dean on Acanthodii.—Order Ichthyotomi. 506 CHAPTER XXX. THE TRUE SHARKS. Order Notidani.—Family