A new era in the history of ichthyology commences with Ray, Willughby and Artedi, who were the first to recognize the true principles by which the natural affinities of animals should be determined. Their labours stand in so intimate a connexion with each other that they represent but one great step in the progress of this science. Ray and Willughby. J. Ray (1628-1705) was the friend and guide of F. Willughby (1635-1672). They found that a thorough reform in the method of treating the vegetable and animal kingdoms had become necessary; that the only way of bringing order into the existing chaos was by arranging the various forms according to their structure. They therefore substituted facts for speculation, and one of the first results of this change, perhaps the most important, was that, having recognized "species" as such, they defined the term and fixed it as the starting-point of all sound zoological knowledge. Although they had divided their work so that Ray attended to the plants principally, and Willughby to the animals, the _Historia piscium_ (Oxf., 1686), which bears Willughby's name on the title-page and was edited by Ray, is their joint production. A great part of the observations contained in it were collected during the journeys they made together in Great Britain and in the various countries of Europe. By the definition of fishes as animals with blood, breathing by gills, provided with a single ventricle of the heart, and either covered with scales or naked, the Cetaceans are excluded. The fishes proper are arranged primarily according to the cartilaginous or the osseous nature of the skeleton, and then subdivided according to the general form of the body, the presence or the absence of ventral fins, the soft or the spinous structure of the dorsal rays, the number of dorsal fins, &c. No fewer than four hundred and twenty species are thus arranged and described, of which about one hundred and eighty were known to the authors from personal examination--a comparatively small proportion, but descriptions and figures still formed in great measure the substitute for our modern collections and museums. With the increasing accumulation of forms, the want of a fixed nomenclature had become more and more felt. Artedi. Peter Artedi (1705-1734) would have been a great ichthyologist if Ray or Willughby had not preceded him. But he was fully conscious of the fact that both had prepared the way for him, and therefore he did not fail to reap every possible advantage from their labours. His work, edited by Linnaeus, is divided as follows:--