Robert Collett.
We may now turn from the universal catalogues to the work on special groups, on local faunas, or on particular branches of the subject of ichthyology. These lines of study were made possible by the work of Cuvier and Valenciennes and especially by that of Dr. Günther.
Before taking up the students of faunal groups, we may, out of chronological order, consider the researches of three great taxonomists, who have greatly contributed to the modern system of the classification of fishes.
Louis Agassiz (born at Motiers in western Switzerland in 1807; died at Cambridge, Mass., in 1873) was a man of wonderful insight in zoological matters and possessed of a varied range of scientific information, scarcely excelled in any age—intellectually a lineal descendant of Aristotle. His first work on fishes was the large folio on the fishes collected by Jean Baptiste Spix (1781-1826) in Brazil, published at Munich in 1827. After his establishment in America in 1846, soon after which date, he became a professor in Harvard University, Agassiz published a number of illuminating papers on the fresh-water fishes of North America. He was the first to recognize the necessity of the modern idea of genera among fishes, and most of the groups designated by him as distinct genera are retained by later writers. He was also the first to investigate the structure of the singular viviparous surf-fishes of California, the names Embiotoca and Holconotus applied to these fishes being chosen by him.
His earlier work, "Recherches sur les Poissons des Eaux Douces," published in Europe, gave a great impetus to our knowledge of the anatomy and especially of the embryology of the fresh-water fishes. Most important of all his zoological publications was the "Recherches sur les Poissons Fossiles," published at Neufchatel from 1833 to 1843. This work laid the foundation of the systematic study of the extinct groups of fishes. The relations of sharks were first appreciated by Agassiz, and the first segregation of the ganoids was due to him. Although he included in this group many forms not truly related either to anything now called ganoids, nor even to the extinct mailed forms which preceded them, yet the definition of this order marked a distinct step in advance.
The great, genial, hopeful personality of Agassiz and his remarkable skill as a teacher made him the "best friend that ever student had" and gave him a large following as a teacher. Among his pupils in ichthyology were Charles Girard (1822-1895), Frederick Ward Putnam, Alexander Agassiz, Samuel Garman, Samuel H. Scudder, and the present writer.
Johannes Müller (1808-1858), of Berlin, was one of the greatest of comparative anatomists. In his revision of Cuvier's "System of Classification" he corrected many errors in grouping, and laid foundations which later writers have not altered or removed. Especially important is his classical work, "Ueber den Bau and die Grenzen der Ganoiden." In this he showed some of the real fundamental characters of that group of archaic fishes, and took from it the most heterogeneous of the elements left in it by Agassiz. To Müller we also owe the first proper definition of the Leptocardii and the Cyclostomata, and, in association with Dr. J. Henle, Müller has given us one of the best general accounts of the sharks ("Systematische Beschriebungen der Plagiostomen"). To Müller we owe an accession of knowledge in regard to the duct of the air-bladder, and the groups called Physostomi, Physoclysti, Dipneusti (Dipnoi), Pharyngognathi, and Anacanthini were first defined by him.
In his work on Devonian fishes, the great British comparative anatomist, Thomas Henry Huxley, first distinguished the group of Crossopterygians, and separated it from the ganoids and dipnoans.
Theodore Nicholas Gill is the keenest interpreter of taxonomic facts yet known in the history of ichthyology. He is the author of a vast number of papers, the first bearing date of 1858, touching almost every group and almost every phase of relation among fishes. His numerous suggestions as to classification have been usually accepted in time by other authors, and no one has had a clearer perception than he of the necessity of orderly methods in nomenclature. Among the orders first defined by Gill are the Eventognathi, Nematognathi, Pediculati, Iniomi, Heteromi, Haplomi, Xenomi, and the group called Teleocephali, originally framed to include all the bony fishes except those which showed peculiar eccentricities or modifications. Dr. Gill's greatest excellence has been shown as a scientific critic. Incisive, candid, and friendly, there is scarcely an investigator in biology, in America, who is not directly indebted to him for critical aid of the highest importance. The present writer cannot too strongly express his own obligations to this great teacher, his master in fish taxonomy. Dr. Gill's work is not centered in any single great treatise, but is diffused through a very large number of brief papers and catalogues, those from 1861 to 1865 mostly published by the Academy of Natural Sciences in Philadelphia, those of recent date by the United States National Museum. For many years Dr. Gill has been identified with the work of the Smithsonian Institution at Washington.