Taxonomy.--Defects in Taxonomy.--Analogy and Homology.--Coues on Classification.--Species as Twigs of a Genealogical Tree.--Nomenclature.--The Conception of Genus and Species.--The Trunkfishes.--Trinomial Nomenclature.--Meaning of Species.--Generalization and Specialization.--High and Low Forms.--The Problem of the Highest Fishes. 367 CHAPTER XXII. THE HISTORY OF ICHTHYOLOGY. Aristotle.--Rondelet.--Marcgraf.--Osbeck.--Artedi.--Linnæus.-- Forskål.--Risso.--Bloch.--Lacépède.--Cuvier.--Valenciennes.-- Agassiz.--Bonaparte.--Günther.--Boulenger.--Le Sueur.--Müller.-- Gill.--Cope.--Lütken.--Steindachner.--Vaillant.--Bleeker.-- Schlegel.--Poey.--Day.--Baird.--Garman.--Gilbert.--Evermann.-- Eigenmann.--Zittel.--Traquair.--Woodward.--Dean.--Eastman.--Hay.-- Gegenbaur.--Balfour.--Parker.--Dollo. 387 CHAPTER XXIII. 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.