With regard to the illustrations, about twenty have been prepared after originals published by Cuvier, J. Müller, Owen, Traquair, Duméril, Cunningham, Hasse, Poey, Siebold, and Gegenbaur. A similar number, representing extinct fishes, have been taken, with the kind permission of the author, from Owen’s “Palæontology.” My best thanks are due also to the Committee of Publications of the Zoological Society, and to the Editors of the “Annals and Magazine of Natural History,” and of the “Journal des Museum Godeffroy,” for the loan of woodcuts illustrating some of my papers on South American fishes and on larval forms. The remainder of the illustrations (about three-fourths) are either original figures, or formed part of the article on ‘Ichthyology’ in the former edition of the “Encyclopædia Britannica.” LONDON, _3d October 1880_. CONTENTS. INTRODUCTORY REMARKS. PAGE FISH DEFINED--ICHTHYOLOGY DEFINED 1 CHAPTER I. HISTORY AND LITERATURE 2 Aristotle, 2--Belon, 4--Salviani, 6--Rondelet, 6--Faunists and Anatomists of the Seventeenth Century, 7--Ray and Willughby, 8--Artedi, 9--Linnæus, 10--Gronow and Klein, 12--Pupils and Successors of Linnæus, 12--Bloch, 13--Lacépède, 15--Anatomists and Faunists preceding Cuvier, 16--Cuvier, 17--Agassiz, 20--J. Müller, 22--Discovery of Ceratodus, 25--Recent publications on Fishes, 26--Latest systematic works, 33. CHAPTER II. TOPOGRAPHICAL DESCRIPTION OF THE EXTERNAL PARTS OF FISHES 35 Form of the body, 35--External parts of the head, 36--Trunk and Tail, 39--Fins; their structure, position, and function, 40--Skin and Scales, 45. CHAPTER III. TERMINOLOGY AND TOPOGRAPHY OF THE SKELETON 51 Axial portion, 51--Vertebra and its parts; terms defined, 51--Skull; bones topographically enumerated, 53--Bones of the limbs, 59--Synonymic list of bones, 59. CHAPTER IV. MODIFICATIONS OF THE SKELETON 63 Branchiostoma, 63--Cyclostomes, 64--Chondropterygians, 66--Holocephali, 70--Ganoids, 71--Dipnoi, 71--Chondrostei, 74--Polypteroidei, 77--Lepidosteoidei, 80--Amioidei, 82--Teleostei, 83--Classification of the bones of the Teleosteous skull according to the vertebral doctrine, 85--their morphological classification, 86--Limb-bones of Teleosteans, 92. CHAPTER V. MYOLOGY 93 General arrangement of the Muscles, 93--Electric organs, 94. CHAPTER VI.