The most noteworthy of those who were active in tropical countries are W. PISO and G. MARGRAV. They accompanied as physicians the Dutch Governor, Prince Moritz of Nassau, to Brazil (1637–44). Margrav especially studied the fauna of the country, and although he died before his return to Europe, his observations were published by his colleague, and embodied in a work “Historia naturalis Braziliæ” (Lugd. 1648, fol.), in which the fourth book treats of the fishes. He describes about 100 species, all of which had been previously unknown, in a manner far superior to that of his predecessors. The accompanying figures are not good, but nearly always recognisable, and giving a fair idea of the form of the fish. Margrav himself, with the aid of an artist, had made a most valuable collection of coloured drawings of the objects observed and described by him, but many years were allowed to pass before it was scientifically utilised by Bloch and others. [Sidenote: Anatomists, 1600–1700.] Of the men who left records of their anatomical researches, we may mention BORELLI (1608–79), who wrote a work “De motu animalium” (Rom. 1680, 4to), in which he explained the mechanism of swimming, and the function of the air-bladder; M. MALPIGHI (1628–94), who examined the optic nerve of the sword-fish; the celebrated J. SWAMMERDAM (1637–80), who described the intestines of numerous fishes; and J. DUVERNEY (1648–1730), who entered into detailed researches of the organs of respiration. * * * * * A new era in the history of Ichthyology commences with _Ray_, _Willughby_, and _Artedi_, who were the first to recognise the true principles by which the natural affinities of animals should be determined. Their labours stand in so intimate a connection with each other that they represent only one stride in the progress of this science. * * * * * [Sidenote: Ray and Willughby] J. RAY (born 1628 in Essex, died 1705), was the friend and guide of F. WILLUGHBY (1635–72). They had recognised that a thorough reform of the treatment of the vegetable and animal kingdoms had become necessary; that the only way of bringing order into the existing chaos was that of arranging the various forms with regard to their structure; that they must cease to be burdened with inapplicable passages and quotations of the ancient writers, and to perpetuate the erroneous or vague notions of their predecessors. They abandoned speculation, and adhered to facts only. One of the first results, and perhaps the most important, of their method was, that having recognised the “species” as such, they defined this term, and fixed it as the base, from which all sound zoological knowledge has to start.