Aristotle's information on the habits of fishes, their migrations, mode and time of propagation, and economic uses is, so far as it has been tested, surprisingly correct. Unfortunately, we too often lack the means of recognizing the species of which he gives a description. His ideas of specific distinction were as vague as those of the nshermen whose nomenclature he adopted; it never occurred to him that vernacular names are subject to change, or may'be entirely lost in course of time, and the difficulty of identifying his species is further increased by the circumstance that sometimes several popular names are applied by him to the same fish, or different stages of growth are designated by distinct names. The number of fishes known to Aristotle seems to have been about one hundred and fifteen, all of which are inhabitants of the Aegean Sea. That one man should have laid so sure a basis for future progress in zoology is less surprising than that for about eighteen centuries a science which seemed to offer particular attractions to men gifted with power of observation was no further advanced. Yet such is the case. Aristotle's successors remained satisfied to be his copiers or commentators, and to collect fabulous stories or vague notions. With few exceptions (such as Ausonius, who wrote a small poem, in which he describes from his own observations the fishes of the Moselle) authors abstained from original research; and it was not until about the middle of the 16th century that ichthyology made a new step in advance by the appearance of Belon, Rondelet and Salviani, who almost simultaneously published their great works, by which the idea of species was established.
P. Belon travelled in the countries bordering on the eastern part of the Mediterranean in the years 1547-1550; he collected Be, , m rich stores of positive knowledge, which he embodied in several works. The one most important for the progress of ichthyology is that entitled De-aquatilibus libri duo (Paris, 1553). Belon knew about one hundred and ten fishes, of which he gives rude but generally recognizable figures. Although Belon rarely gives definitions of the terms used by him, it is not generally very difficult to ascertain the limits which he intended to assign to each division of aquatic animals. He very properly divides them into such as are provided with blood and those without it-two divisions corresponding in modern language to vertebrate and invertebrate aquatic animals. The former are classified by him according to size, the further subdivisions being based on the structure of the skeleton, mode of propagation, number of limbs, form of the body and physical character of the habitat.
The work of the Roman ichthyologist H. Salviani (1514-1 572), bears evidence of the high social position which the author S, ,', , m, held as physician to three popes. Its title is Aquatilium ammalzum hzslorza (Rome, 1554-1557, fol.). It treats exclusively of the fishes of Italy. Ninety-two species are figured on seventy-six plates, which, as regards artistic execution, are masterpieces of that period, although those specific characteristics which nowadays constitute the value of a Zoological drawing were overlooked by the author or artist. No attempt is made at a natural classification, but the allied forms are generally placed in
close proximity. The descriptions are equal to those given by Belon, entering much into the details of the economy and uses of the several species, and were evidentl com osed with the
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view of collecting in a readable form all that might interest to the class of society in which the author Salviani's work is of a high order. It could not fail to render ichthyology popular in the country to the fauna of which it was devoted, but it was not fitted to advance ichthyology as a science generally; in this respect Salviani is not to be compared with Rondelet or Belon.
G. Rondelet (1507-1557) had the great advantage over Belon of having received a medical education at Paris, and especially Rondelet of having gone through a complete course of instruction in anatomy as a pupil of Guentherus of Andernach. l' his is conspicuous throughout his works-Libri de piscibus murinis (Lyons. 1554); and Uzziiwsan (I(]7Lt1[1:lf1f7}'lf /zistnriuc pars tzllera (Lyons, 15551. Nevertheless they cannot be regarded as more than considerably enlarged editions of Belon's work. For, although he worked independently of the latter, the system adopted by him is characterized by the same absence of the true principles of classification. His work is almost entirely limited to European and chiefly to Mediterranean forms, and comprises no fewer than one hundred and ninety-seven marine and forty seven fresh-water fishes. His descriptions are more complete and his figures much more accurate than those of Belon; and the specific account is preceded by introductory chapters, in which he treats in a general manner of the distinctions, the external and internal parts, and the economy of fishes. Like Belon, he had no conception of the various categories of classification-com founding throughout his work the terms “ genus ” and “ species, ” but he had an intuitive notion of what his successors called a “ species, ” and his principal object was to give as much information as possible regarding such species.
For nearly a century the works of Belon and Rondelet continued to be the standard works on ichthyology; but the science did not remain stationary during that period. The attention of naturalists was now directed to the fauna of foreign countries, especially of the Spanish and Dutch possessions in the New World; and in Europe the establishment of anatomical schools and academies led to careful investigation of the internal anatomy of the most remarkable European forms. Limited as these efforts were as to their scope, they were sufficiently numerous to enlarge the views of naturalists, and to destroy that fatal dependence on preceding authorities which had kept in bonds even Rondelet and Belon. The most noteworthy of those engaged in these inquiries in tropical countries were W. Piso and G. Marcgrave, who accompanied as physicians the Dutch governor, Count Maurice of Nassau, to Brazil (1630-1644). Of the men who left records of their anatomical researches, we may mention Borelli (1608-1679), who wrote a work De motu animalium (Rome, 1680, 4to), in which he explained the mechanism of swimming and the function of the air-bladder; M. Malpighi (1628-1694), who examined the optic nerve of the sword-fish; the celebrated J. Swammerdam (1637-1680), who described the intestines of numerous fishes; and ]. Duverney (1648-1730), who investigated in detail the organs of respiration. 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.
J. Ray (1628-1705) was the friend and guide of F. Willughby (163 5-1672). 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 la;-}: ””d order into the existing chaos was by arranging the;, , gl, ;, y 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. l-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