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Bible Encyclopedias

1911 Encyclopedia Britannica

Ichneumon-Fly

A general name applied to parasitic insects of the section Ichneumonoidea (or Entomophaga ), order 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.

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 Artedi 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: (i) In the Bibliotheca ichthyologica Artedi gives a very complete list of all preceding authors who had written on fishes, with a critical analysis of their works. (2) The Philosophia ichthyologica is devoted to a description of the external and internal parts of fishes; Artedi fixes a precise terminology for all the various modifications of the organs, distinguishing between those characters which determine a genus and such as indicate a species or merely a variety; in fact he establishes the method and principles which subsequently have guided every systematic ichthyologist. (3) The Genera piscium contains well-defined diagnoses of forty-five genera, for which he has fixed an unchangeable nomenclature. (4) In the Species piscium descriptions of seventy-two species, examined by himself, are given - descriptions which even now are models of exactitude and method. (5) Finally, in the Synonymia piscium references to all previous authors are arranged for every species, very much in the manner which is adopted in the systematic works of the present day.

Artedi has been justly called the father of ichthyology. So admirable was his treatment of the subject, that even Linnaeus could only modify and add to it. Indeed, so far as ichthyology is concerned, Linnaeus has scarcely done anything beyond applying binominal terms to the species properly described and classified by Artedi. His classification of the genera appears in the 12th edition of the Systema thus: A. Amphibia nantia. - Spiraculis compositis. - Petromyzon, Raia, Squalus, Chimaera. Spiraculis solitariis. - Lophius, Acipenser, Cyclopterus, Baiistes, Ostracion, Tetrodon, Diodon, Centriscus, Syngnathus, Pegasus.

1 B. Pisces codes

2 C. Pisces jugulares.

3 D. Pisces thoracici

4 E. Pisces abdominales

5 Authorities

6 External Features

7 Head, Trunk and Tail

8 Fins

9 Cement Organs

10 Photogenic Organs

11 External Gills

12 Alimentary Canal

13 Lung

14 Function

15 Pyloric Caeca

16 Coelomic Organs

17 Electrical Organs. 4

18 Nephridial System

19 Gonads

20 Dipneusti

21 Teleostomi

22 Organs of the Mesenchyme

23 Skeletal System

24 1. Chordal Skeleton

25 2. Cartilaginous or Chondral Skeleton

26 Ribs

27 Median Fin Skeleton

28 Osseous or Bony Skeleton

29 Teeth

30 Teleostei

31 sphot f? socc

32 Appendicular Skeleton

33 Vascular System

34 I

35 Arterial System

36 Pulmonary Veins

37 Central Nervous System

38 Spinal Cord

39 Brain

40 Selachians

41 Teleostei

42 Sense Organs

43 Peripheral Nerves

44 Trigeminus (V.)

45 Lateralis Group of Nerves

46 Sympathetic

47 2. Pelagic Fishe

48 3. Deep-Sea Fishe

49 The Palaearctic or Europaeo - Asiatic Region

B. Pisces codes

Muraena, Gymnotus, Trichiurus, Anarrhichas, Ammodytes, Ophidium, Stromateus, Xiphias.

C. Pisces jugulares.

Callionymus, Uranoscopus, Trachinus, Gadus, Blennius.

D. Pisces thoracici

Cepola, Echeneis, Coryphaena, Gobius, Cottus, Scorpaena, Zeus, Pleuronectes, Chaetodon, Sparus, Labrus, Sciaena, Perca, Gasterosteus, Scomber, Mullus, Trigla.

E. Pisces abdominales

Cobitis, Amia, Silurus, Teuthis, Loricaria, Salmo, Fistularia, Esox, Elops, Argentina, Atherina, Mugil, Mormyrus, Exocoetus, Polynemus, Clupea, Cyprinus.

Two contemporaries of Linnaeus, L. T. Gronow and J. T. Klein, attempted a systematic arrangement of fishes.

The works of Artedi and Linnaeus led to an activity of research, especially in Scandinavia, Holland, Germany and England, such as has never been equalled in the history of biological science. Whilst some of the pupils and followers of Linnaeus devoted themselves to the examination and study of the fauna of their native countries, others proceeded on voyages of discovery to foreign and distant lands. Of these latter the following may be especially mentioned: O. Fabricius worked out the fauna of Greenland; Peter Kalm collected in North America, F. Hasselquist in Egypt and Palestine, M. T. Briinnich in the Mediterranean, Osbeck in Java and China, K. P. Thunberg in Japan; Forskal examined and described the fishes of the Red Sea; G. W. Steller, P. S. Pallas, S. G. Gmelin, and A. J. Giildensta.dt traversed nearly the whole of the Russian empire in Europe and Asia. Others attached themselves as naturalists to celebrated navigators, such as the two Forsters (father and son) and Solander, who accompanied Cook; P. Commerson, who travelled with Bougainville; and Pierre Sonnerat. Of those who studied the fishes of their native countries, the most celebrated were Pennant (Great Britain), O. F. Milner (Denmark), Duhamel du Monceau (France), C. von Meidinger (Austria), J. Cornide (Spain), and A. Parra (Cuba).

The mass of materials brought together was so great that, not long after the death of Linnaeus, the necessity made itself felt for collecting them in a compendious form. Several compilers undertook this task; they embodied the recent discoveries in new editions of the classical works of Artedi and Linnaeus, but, they only succeeded in burying those noble monuments under a chaotic mass of rubbish. For ichthyology it was fortunate that two men at least, Bloch and Lacepede, made it a subject of prolonged original research.

Mark Eliezer Bloch (1723-1799), a physician of Berlin, had reached the age of fifty-six when he began to write on ichthyological subjects. His work consists of two divisions: - (1) beconomische Naturgeschichte der Fische Deutsch- lands (Berl., 1782-1784); (2) Naturgeschichte der ausldndischen Fische (Berl., 1785-1795). The first division, which is devoted to a description of the fishes of Germany, is entirely original. His descriptions as well as figures were made from nature, and are, with few exceptions, still serviceable; indeed many continue to be the best existing in literature. Bloch was less fortunate, and is much less trustworthy, in his natural history of foreign fishes. For many of the species he had to trust to more or less incorrect drawings and descriptions by travellers; frequently, also, he was deceived as to the origin of specimens which he purchased. Hence his accounts contain numerous errors, which it would have been difficult to correct had not nearly the whole of the materials on which his work is based been preserved in the collections at Berlin.

After the completion of his great work Bloch prepared a general system of fishes, in which he arranged not only those previously described, but also those with which he had afterwards become acquainted. The work was ably edited and published after Bloch's death by a philologist, J. G. Schneider, under the title M. E. Blochii Systema ichthyologiae iconibus cx. illustratum (Berl., 1801). The number of species enumerated amounts to 1519. The system is based upon the number of the fins, the various orders being termed Hendecapterygii, Decapterygii, &c. An artificial method like this led to the most unnatural combinations and distinctions.

Bloch's Naturgeschichte remained for many years the standard work. But as regards originality of thought Bloch was far surpassed by his contemporary, B. G. E. de Lacepede, born at Agen, in France, in 1756, who became professor at the museum of natural history in Paris, where he died in 1825.

Lacepede had to contend with great difficulties in the preparations of his Histoire des poissons (Paris, 1798-1803, 5 vols.), which was written during the most disturbed period of the French Revolution. A great part of it was composed whilst the author was separated from collections and books, and had to rely on his notes and manuscripts only. Even the works of Bloch and other contemporaneous authors remained unknown or inaccessible to him for a long time. His work, therefore, abounds in the kind of errors into which a compiler is liable to fall. Thus the influence of Lacepede on the progress of ichthyology was vastly less than that of his fellow-labourer; and the labour laid on his successors in correcting numerous errors probably outweighed the assistance which they derived from his work.

The work of the principal students of ichthyology in the period between Ray and Lacepede was chiefly systematizing and describing; but the internal organization of fishes also received attention from more than one great anatomist. Albrecht von Haller, Peter Camper and John Hunter examined the nervous system and the organs of sense; and Alexander Monro, secundus, published a classical work, The Structure and Physiology of Fishes Explained and Compared with those of Man and other Animals (Edin., 1785). The electric organs of fishes ( Torpedo and Gymnotus ) were examined by Reaumur, J. N. S. Allamand, E. Bancroft, John Walsh, and still more exactly by J. Hunter. The mystery of the propagation of the eel called forth a large number of essays, and even the artificial propagation of Salmonidae was known and practised by J. G. Gleditsch (1764).

Bloch and Lacepede's works were almost immediately succeeded by the labours of Cuvier, but his early publications were tentative, preliminary and fragmentary, so that some little time elapsed before the spirit infused into ichthyology by this great anatomist could exercise its influence on all the workers in this field.

The Descriptions and Figures of Two Hundred Fishes collected at Vizagapatam on the Coast of Coromandel (Lond., 1803, 2 vols.) by Patrick Russel, and An Account of the Fishes found in the River Ganges and its Branches (Edin., 1822, 2 vols.) by F. Hamilton (formerly Buchanan), were works distinguished by greater accuracy of the drawings (especially the latter) than was ever attained before. A Natural History of British Fishes was published by E. Donovan (Lond., 1802-1808); and the Mediterranean fauna formed the study of the lifetime of A. Risso, Ichthyologie de Nice (Paris, 1810); and Histoire naturelle de l'Europe meridionale (Paris, 1827). A slight beginning in the description of the fishes of the United States was made by Samuel Latnam Mitchill (1764-1831), who published, besides various papers, a Memoir on the Ichthyology of New York, in 1815.

G. Cuvier (1769-1832) devoted himself to the study of fishes with particular predilection. The investigation of their anatomy, and especially of their skeleton, was continued until Cuvien he had succeeded in completing so perfect a framework of the system of the whole class that his immediate successors required only to fill up those details for which their master had had no leisure. He ascertained the natural affinities of the infinite variety of forms, and accurately defined the divisions, orders, families and genera of the class, as they appear in the various editions of the Regne Animal. His industry equalled his genius; he formed connections with almost every accessible part of the globe; and for many years the museum of the Jardin des Plantes was the centre where all ichthyological treasures were deposited. Thus Cuvier brought together a collection which, as it contains all the materials on which his labours were based, must still be considered as the most important. Soon after the year 1820, Cuvier, assisted by one of his pupils, A. Valenciennes, commenced his great work on fishes, Historie naturelle des Poissons, g > > of which the first volume appeared in 1828. After Cuvier's death in 1832 the work was left entirely in the hands of Valenciennes, whose energy and interest gradually slackened, rising to their former pitch in some parts only, as, for instance, in the treatise, on the herring. He left the work unfinished with the twenty-second volume (1848), which treats of the Salmonoids. Yet, incomplete as it is, it is indispensable to the student.

The system finally adopted by Cuvier is the following: - A. Poissons Osseux.

I. A Branchies En Peignes Ou En Lames.

I. A Mdchoire Superieure Libre. a. Acanthopterygiens. Percoides. Sparoldes. Branchies labyrinthiques.

Polynemes. ChetodonoIdes. Lophioides.

Mulles. Scomberoides. Gobioides.

Joues cuirassees Muges. Labroides. Scienoides.

b. Malacopterygiens. Abdominaux. Subbrachiens. Apodes. Cyprinoides. Gadoides. Murenoides.

Siluroides. Pleuronectes.

Salmonoides. Discoboles.

Clupeoides.

Lucioides.

2. A Mdchoire Superieure Fixee. Selerodermes. Gymnodontes.

II. A Branchies En Forme De Houppes.

Lophobranches.

B. Cartilagineux Ou Chondropterygiens.

Sturioniens. Plagiostomes. Cyclostomes.

We have only to compare this system with that of Linnaeus if we wish to measure the gigantic stride made by ichthyology during the intervening period of seventy years. The various characters employed for classification have been examined throughout the whole class, and their relative importance has been duly weighed and understood. The important category of " family " appears now in Cuvier's system fully established as intermediate between genus and order. Important changes in Cuvier's system have been made and proposed by his successors, but in the main it is still that of the present day.

Cuvier had extended his researches beyond the living forms, into the field of palaeontology; he was the first to observe the close resemblance of the scales of the fossil Palaeoniscus to those of the living Polypterus and Lepidosteus, the prolongation and identity of structure of the upper caudal lobe in Palaeoniscus and the sturgeons, the presence of peculiar " fulcra " on the anterior margin of the dorsal fin in Palaeoniscus and Lepidosteus, and inferred from these facts that the fossil genus was allied either to the sturgeons or to Lepidosteus. But it did not occur to him that there was a close relationship between those recent fishes. Lepidosteus and, with it, the fossil genus remained in his system a member of the order of Malacopterygii abdominales. It was left to L. Agassiz (1807-1873) to point out the importance of the structure of the scales as a characteristic, and to open a path towards the knowledge of a whole new subclass A of fishes, the Ganoidei. Impressed with the fact that the peculiar scales of Polypterus and Lepidosteus are common to all fossil osseous fishes down to the Chalk, he takes the structure of the scales generally as the base for an ichthyological system, and distinguishes four orders: 1. Placoids. - Without scales proper, but with scales of enamel, sometimes large, sometimes small, and reduced to mere points (Rays, Sharks and Cyclostomi, with the fossil Hybodontes). 2. Ganoids.- With angular bony scales, covered with a thick stratum of enamel: to this order belong the fossil Lepidoides, Sauroides, Pycnodontes and Coelacanthi; the recent Polypterus, Lepidosteus, Sclerodermi, Gymnodontes, Lophobranches and Siluroides; also the Sturgeons. 3. Ctenoids. - With rough scales, which have their free margins denticulated: Chaetodontidae, Pleuronectidae, Percidae, Polyacanthi, Sciaenidae, Sparidae, Scorpaenidae, Aulostomi. 4. Cycloids. - With smooth scales, the hind margin of which lacks denticulation: Labridae, Mugilidae, Scombridae, Gadoidei, Gobiidae, Muraenidae, Lucioidei, Salmonidae, Clupeidae, Cyprinidae.

If Agassiz had had an opportunity of acquiring a more extensive and intimate knowledge of existing fishes before his energies were absorbed in the study of fossil remains, he would doubtless have recognized the artificial character of his classification. The distinctions between cycloid and ctenoid scales, between placoid and ganoid fishes, are vague, and can hardly be maintained. So far as the living and post-Cretacean forms are concerned, he abandoned the vantage-ground gained by Cuvier; and therefore his system could never supersede that of his predecessor, and finally shared the fate of every classification based on the modifications of one organ only. But Agassiz opened an immense new field of research by his study of the infinite variety of fossil forms. In his principal work, Recherches sur les poissons fossiles, Neuchatel, 1833-1843, 4to, atlas in fol., he placed them before the world arranged in a methodical manner, with excellent descriptions and illustrations. His power of discernment and penetration in determining even the most fragmentary remains is astonishing; and, if his order of Ganoids is an assemblage of forms very different from what is now understood by that term, he was the first who recognized that such an order of fishes exists.

The discoverer of the Ganoidei was succeeded by their explorer Johannes Muller (1801-1858). In his classical memoir Ober den Bau and die Grenzen der Ganoiden (Berl., 1846) he showed that the Ganoids differ from all the other osseous fishes, and agree with the Plagiostomes, in the structure of the heart. By this primary character, all heterogeneous elements, as Siluroids, Osteoglossidae, &c., were eliminated from the order as understood by Agassiz. On the other hand, he did not recognize the affinity of Lepidosiren to the Ganoids, but established for it a distinct subclass, Dipnoi, which he placed at the opposite end of the system. By his researches into the anatomy of the lampreys and Amphioxus, their typical distinctness from other cartilaginous fishes was proved; they became the types of two other subclasses, Cyclostomi and Leptocardii. Muller proposed several other modifications of the Cuvierian system; and, although all cannot be maintained as the most natural arrangements, yet his researches have given us a much more complete knowledge of the organization of the Teleostean fishes, and later inquiries have shown that, on the whole, the combinations proposed by him require only some further modification and another definition to render them perfectly natural.

The discovery (in the year 1871) of a living representative of a genus hitherto believed to be long extinct, Ceratodus, threw a new light on the affinities of fishes. The writer of the present article, who had the good fortune to examine this fish, was enabled to show that, on the one hand, it was a form most closely allied to Lepidosiren, and, on the other, that it could not be separated from the Ganoid fishes, and therefore that Lepidosiren also was a Ganoid,-a relation already indicated by Huxley in a previous paper on " Devonian Fishes." Having followed the development of the ichthyological system down to this period, we now enumerate the most important contributions to ichthyology which appeared contemporaneously with or subsequently to the publication of the great work of Cuvier and Valenciennes. For the sake of convenience we may arrange these works under two heads.

I. Voyages, Containing General Accounts Of Zoological Collections A. French.-i. Voyage autour du monde sur les corvettes de S. M. l'Uranie et la Physicienne, sous le commandement de M. Freycinet, " Zoologie-Poissons," par Quoy et Gaimard (Paris, 1824). 2. Voyage de la Coquille, " Zoologie," par Lesson (Paris, 1826-1830).

3. Voyage de l'Astrolabe, sous le commandement de M. J. Dumont d'Urville, " Poissons," par Quoy et Gaimard (Paris, 18 34). 4. Voyage au Pole Sud par M. J. Dumont d'Urville, " Poissons," par Hombron et Jacquinot (Paris, 1853-1854).

B. English.-i. Voyage of H.M.S. Sulphur, " Fishes," by J. Richardson (Lond., 1844-1845). 2. Voyage of H.M.SS. Erebus and Terror, " Fishes," by J. Richardson (Lond., 1846). 3. Voyage of H.M.S. Beagle, " Fishes," by L. Jenyns (Lond., 1842).

C. German. Reise der osterreichischen Fregatte Novara, " Fische," von R. Kner (Vienna, 1865).

II. [[Faunae A]]. Great Britain.-i. R. Parnell, The Natural History of the Fishes of the Firth of Forth (Edin., 1838). 2. W. Yarrell, A History of British Fishes (3rd ed., Lond., 18 59). 3. J. Couch, History of the Fishes of the British Islands (Lond., 1862-1865).

B. Denmark and Scandinavia.-i. H. Kroyer, Danmark's Fiske (Copenhagen, 1838-1853). 2. S. Nilsson, Skandinavisk Fauna, vol. iv. " Fiskarna " (Lund, 18 55). 3. Fries och Ekstrom, Skandinaviens Fiskar (Stockh., 1836).

C. Russia.-i. Nordmann, " Ichthyologie pontique," in Demidoff's Voyage dans la Russie meridionale, tome iii. (Paris, 1840).

Germany Heckel and Kner, Die Susswasserfische der osterreichischen Monarchie (Leipz., 1858). 2. C. T. E. Siebold, Die Susswasserfische von Mitteleuropa (Leipz., 1863).

E. Italy and Mediterranean.-i. Bonaparte, Iconografia della fauna italica, tom iii., " Pesci " (Rome, 1832-1841). 2. Costa, Fauna del regno di Napoli, " Pesci " (Naples, about 1850).

F. France.-i. E. Blanchard, Les Poissons des eaux douces de la France (Paris, 1866).

G. Spanish Peninsula.-The fresh-water fish fauna of Spain and Portugal was almost unknown, until F. Steindachner paid some visits to those countries for the purpose of exploring the principal rivers. His discoveries are described in several papers in the Sitzungsberichte der Akademie zu Wien. B. du Bocage and F. de B. Capello made contributions to our knowledge of the marine fishes on the coast of Portugal ( Jorn. Scienc. Acad. Lisb.). H. North America.-i. J. Richardson, Fauna Boreali-Americana, part iii., " Fishes " (Lond., 1836). The species described in this work are nearly all from the British possessions in the north. 2. Dekay, Zoology of New York, part iv., " Fishes " (New York, 1842). 3. Reports of the United States Commission of Fish and Fisheries (5 vols., Washington, 1873-1879) contain much valuable information. Besides these works, numerous descriptions of North American fresh-water fishes have been published in the reports of the various U.S. Government expeditions, and in North American scientific journals, by D. H. Storer, S. F. Baird, C. Girard, W. O. Ayres, E.

D. Cope, D. S. Jordan, G. Brown Goode, &c.

Japan. Fauna Japonica, " Poissons," par H. Schlegel, (Leiden, 1850).

J. East Indies; Tropical parts of the Indian and Pacific Oceans.- 1. E. Ruppell, Atlas zu der Reise imnordlichenAfrika (Frankf., 1828).

2. E. Ruppell, Neue Wirbelthiere, " Fische " (Frankf., 1 837). 3. R. L. Playfair and A. Gunther, The Fishes of Zanzibar (Lond., 1876). 4. C. B. Klunzinger, Synopsis der Fische des Rothen Meers (Vienna, 1870-1871). 5. F. Day, The Fishes of India (Lond., 1865, 4to) contains an account of the fresh-water and marine species. 6. A. Gunther, Die Fische der Sildsee (Hamburg, 4to), from 1873 (in progress). 7. Unsurpassed in activity, as regards the exploration of the fish fauna of the East Indian archipelago, is P. Bleeker (1819-1878), a surgeon in the service of the Dutch East Indian Government, who, from the year 1840, for nearly thirty years, amassed immense collections of the fishes of the various islands, and described them in extremely numerous papers, published chiefly in the journals of the Batavian Society. Soon after his return to Europe (1860) Bleeker commenced to collect the final results of his labours in a grand work, illustrated by coloured plates, Atlas ichthyologique des Indes Orientales Neerlandaises (Amsterd., fol., 1862), the publication of which was interrupted by the author's death in 1878.

Africa. A. Gunther, " The Fishes of the Nile," in Petherick's Travels in Central Africa (Lond., 1869). 2. W. Peters, Naturwissenschaftliche Reise nach Mossambique, iv., " Flussfische " (Berl., 1868, 4to).

L. West Indies and South America.-i. L. Agassiz, Selecta genera et species piscium, quae in itinere per Brasiliam collegit J. B. de Spix (Munich, 1829, fol.). 2. F. de Castelnau, Animaux nouveaux ou rares, recueillis pendant l'expedition dans les parties centrales de l'Amerique du Sud, " Poissons " (Paris, 1 855). 3. L. Vaillant and F. Bocourt, Mission scientifique au Mexique et dans l'Amerique centrale, " Poissons " (Paris, 1874). 4. F. Poey, the celebrated naturalist of Havana, devoted many years of study to the fishes of Cuba. His papers and memoirs are published partly in two periodicals, issued by himself, under the title of Memorias sobre la historia natural de la isla de Cuba (from 1851), and Repertorio fisico-natural de la isla de Cuba (from 1865), partly in North American scientific journals. And, finally, F. Steindachner and A. Gunther have published many contributions, accompanied by excellent figures, to our knowledge of the fishes of Central and South America.

M. New Zealand. F. W. Hutton and J. Hector, Fishes of New Zealand (Wellington, 1872).

N. Arctic Regions.-i. C. Li tken, " A Revised Catalogue of the Fishes of Greenland," in Manual of the Natural History, Geology and Physics of Greenland (L9nd., 1875, 8vo). 2. The fishes of Spitzbergen were examined by A. J. Malmgren (1865). (A. C. G.) II. History And Literature From 1880 In the systematic account which followed the above chapter in the 9th edition of the Encyclopaedia Britannica, the following classification, which is the same as that given in the author's Introduction to the Study of Fishes (London, 1880) was adopted by Albert Gunther: Subclass I.: Palaeichthyes.

Order I.: Chondropterygii. With two suborders: Plagiostomata and Holocephala. Order II.: Ganoidei. With eight suborders: Placodermi, Acanthodini, Dipnoi, Chondrostei, Polypteroidei, Pycnodontoidei, Lepidosteoidei, Amioidei.

Subclass II.: Teleostei.

Order I.: Acanthopterygii. With the divisions Perciformes, Beryciformes, Kurtiformes, Polynemiformes, Sciaeniformes, Xiphiiformes, Trichiuriformes, Cotto-Scombriformes, Gobiiformes, Blenniformes, Mugiliformes,Gastrosteiformes, Centrisciformes, Gobiesociformes, Channiformes, Labyrinthibranchii, Lophotiformes, Taeniiformes and Notacanthiformes.

Order II.: Acanthopterygii Pharyngognathi. Order III.: Anacanthini. With two divisions: Gadoidei and Pleuronectoidei. Order IV.: Physostomi. Order V.: Lophobranchii. Order VI.: Plectognathi. Subclass III.: Cyclostomata.

Subclass IV.: Leptocardii.

It was an artificial system, in which the most obvious relationships of the higher groups were lost sight of, and the results of the already fairly advanced study of the fossil forms to a great extent discarded. This system gave rise to much adverse criticism; as T. H. Huxley forcibly put it in a paper published soon after (1883), opposing the division of the main groups into Palaeichthyes and Teleostei: " Assuredly, if there is any such distinction to be drawn on the basis of our present knowledge among the higher fishes, it is between the Ganoids and the Plagiostomes, and not between the Ganoids and the Teleosteans "; at the same time expressing his conviction, " first, that there are no two large groups of animals for which the evidence of a direct genetic connexion is better than in the case of the Ganoids and the Teleosteans; and secondly, that the proposal to separate the Elasmobranchii (Chondropterygii of Gunther), Ganoidei and Dipnoi of Muller into a group apart from, and equivalent to, the Teleostei appears to be inconsistent with the plainest relations of these fishes." This verdict has been endorsed by all subsequent workers at the classification of fishes.

Gunther's classification would have been vastly improved had he made use of a contribution published as early as 1871, but not referred to by him. As not even a passing allusion is made to it in the previous chapter, we must retrace our steps to make good this striking omission. Edward Drinker Cope (1840-1897) was a worker of great originality and relentless energy, who, in the sixties of the last century, inspired by the doctrine of evolution, was one of the first to apply its principles to the classification of vertebrates. Equally versed in recent and fossil zoology, and endowed with a marvellous gift, or " instinct " for perceiving the relationship of animals, he has done a great deal for the advance of our knowledge of mammals, reptiles and fishes. Although often careless in the working out of details and occasionally a little too bold in his deductions, Cope occupies a high rank among the zoologists of the 19th century, and much of his work has stood the test of time.

The following was Cope's classification, 1871 Soc. xiv. 449).

Subclass I. Holocephali.

„ II. Selachii.

„ III. Dipnoi.

„ IV. Crossopterygia, with two orders: Haplistia and Cladistia.

„ V. Actinopteri.

The latter is subdivided in the following manner: Tribe I.: Chondrostei.

Two orders: Selachostomi and Glaniostomi.

Tribe II.: Physostomi.

Twelve orders: Ginglymodi, Halecomorphi, Nematognathi, Scyphophori, Plectospondyli, Isospondyli, Haplomi, Glanen cheli, Ichthyocephali, Holostomi, Enchelycephali, Colocephali. Tribe III.: Physoclysti.

Ten orders: Opisthomi, Percesoces, Synentognathi, Hemibranchii, Lophobranchii, Pediculati, Heterosomata, Plectognathi, Percomorphi, Pharyngognathi.

Alongside with so much that is good in this classification, there are many suggestions which cannot be regarded as improvements on the views of previous workers. Attaching too great an importance to the mode of suspension of the mandible, Cope separated the Holocephali from the Selachii and the Dipnoi from the Crossopterygii, thus obscuring the general agreement which binds these groups to each other, whilst there is an evident want of proportion in the five subclasses. The exclusion from the class Pisces of the Leptocardii, or lancelets, as first advocated by E. Haeckel, was a step in the right direction, whilst that of the Cyclostomes does not seem called for to such an authority as R. H. Traquair, with whom the writer of this review entirely concurs.

The group of Crossopterygians, first separated as a family from the other Ganoids by Huxley, constituted a fortunate innovation, and so was its division into two minor groups, by which the existing forms (Polypteroidei ) were separated as Cladistia. The divisions of the Actinopteri, which includes all Teleostomes other than the Dipneusti and Crossopterygii also showed, on the whole, a correct appreciation of their relationships, the Chondrostei being well separated from the other Ganoids with which they were generally associated. In the groupings of the minor divisions, which Cope termed orders, we had a decided improvement on the Cuvierian-Miillerian classification, the author having utilized many suggestions of his fellow countrymen Theodore Gill, who has done much towards a better understanding of their relationships. In the association of the Characinids with the Cyprinids (Plectospondyli) in the separation of the flat-fishes from the Ganoids, in the approximation of the Lophobranchs to the sticklebacks and of the Plectognaths to the Acanthopterygians, and in many other points, Cope was in advance of his time, and it is to be regretted that his contemporaries did not more readily take up many of his excellent suggestions for the improvement of their systems.

In the subsequent period of his very active scientific life, Cope made many alterations to his system, the latest scheme published by him being the following (" Synopsis of the families of Vertebrata," Amer. Natur., 1889, p. 849) Class: Agnatha. I. Subclass: Ostracodermi.

Orders: Arrhina, Diplorrhina.

II. Subclass: Marsipobranchii. Orders: Hyperotreti, Hyperoarti. Class: Pisces. I. Subclass: Holocephali.

II. Subclass: Dipnoi.

III. Subclass: Elasmobranchii.

Orders: Ichthyotomi, Selachii.

IV. Subclass: Teleostomi.

(i.) Superorder: Rhipidopterygia. Orders: Rhipidistia, Actinistia.

(ii.) Superorder: Crossopterygia. Orders: Placodermi, Haplistia, Taxistia, Cladistia.

(iii.) Superorder: Podopterygia (Chondrostei).

(iv.) Superorder: Actinopterygia. Orders: Physostomi, Physoclysti.

This classification is that followed, with many emendations, by A. S. Woodward in his epoch-making Catalogue of Fossil Fishes (4 vols., London, 1889-1901), and in his most useful Outlines of Vertebrate Paleontology (Cambridge, 1898), and was adopted by Gunther in the 10th edition of the Encyclopaedia Britannica:- Class: Agnatha.

I. Subclass: Cyclostomi.

With three orders: (a) Hyperoartia (Lampreys); ( b) Hyperotreti (Myxinoids); ( c) Cycliae (Palaeospondylus).

II. Subclass: Ostracodermi.

With four orders: (a) Heterostraci (Coelolepidae, Psammosteidae, Drepanaspidae, Pteraspidae); ( b) Osteostraci (Cephalaspidae, Ateleaspidae, &c.); ( c) Antiarchi (Asterolepidae, Pterichthys, Bothrolepis, &c.); ( d) Anaspida (Birkeniidae).

Class: Pisces.

I. Subclass: Elasmobranchii.

With four orders: (a) Pleuropterygii (Cladoselache); ( b) Ichthyotomi (Pleuracanthidae); ( c) Acanthodii (Diplacanthidae, and Acanthodidae); ( d) Selachii (divided from the structure of the vertebral centres into Asterospondyli and Tectospondyli).

II. Subclass: Holocephali.

With one order: Chimaeroidei. III. Subclass: Dipnoi.

With two orders: (a) Sirenoidei (Lepidosiren, Ceratodus, Uronemidae, Ctenodontidae); ( b) Arthrodira (Homosteus, Coccosteus, Dinichthys).

IV. Subclass: Teleostomi.

A. Order: Crossopterygii. With four suborders: (I) Haplistia (Tarassius); (2) Rhipidistia (Holoptychidae, Rhizodontidae, Osteolepidae); (3) Actinistia (Coelacanthidae); (4) Cladistia (Polypterus).

B. Order: Actinopterygii. With about twenty suborders: (I) Chondrostei (Palaeoniscidae, Platysomidae, Chondrosteidae, Sturgeons); (2) Protospondyli (Semionotidae, Macrosemiidae, Pycnodontidae, Eugnathidae, Amiidae, Pachycormidae); (3) Aetheospondyli (Aspidorhynchidae, Lepidosteidae); (4) Isospondyli (Pholidophoridae, Osteoglossidae, Clupeidae, Leptolepidae, &c.); (5) Plectospondyli(Cyprinidae, Characinidae); (6) Nematognathi; (7) Apodes; and the other Teleosteans.

There are, however, grave objections to this system, which cannot be said to reflect the present state of our knowledge. In his masterly paper on the evolution of the Dipneusti, L. Dollo has conclusively shown that the importance of the autostyly on which the definition of the Holocephali from the Elasmobranchii or Selachii and of the Dipneusti from the Teleostomi rested, had been exaggerated, and that therefore the position assigned to these two groups in Gunther's classification of 1880 still commended itself. Recent work on Palaeospondylus, on the Ostracoderms, and on the Arthrodira, throws great doubt on the propriety of the positions given to them in the above classification, and the rank assigned to the main divisions of the Teleostomi do not commend themselves to the writer of the present article, who would divide the fishes into three subclasses: - I. Cyclostomi II. Selachii III. Teleostomi, the characters and contents of which will be found in separate articles; in the present state of uncertainty as to their position, Palaeospondylus and the Ostracodermi are best placed hors cadre and will be dealt with under these names.

The three subclasses here adopted correspond exactly with those proposed in Theo. Gill's classification of the recent fishes (" Families and Subfamilies of Fishes," Mem. Nat. Ac. Sci. vi. 1893), except that they are regarded by that authority as classes.

The period dealt with in this chapter, ushered in by the publication of Giinther's Introduction to the Study of Fishes, has been one of extraordinary activity in every branch of ichthyology, recent and fossil. A glance at the Zoological Record, published by the Zoological Society of London, will show the ever-increasing number of monographs, morphological papers and systematic contributions, which appear year after year. The number of new genera and species which are being proposed is amazing, but it is difficult to tell how many of them will simply go to swell the already overburdened synonymy. Perhaps a reasonable estimate of the living species known at the present day would assess their number at about 13,000.

It is much to be regretted that there is not a single general modern systematic work on fishes. The most important treatises, the 7th volume of the Cambridge Natural History, by T. W. Bridge and G. A. Boulenger, and D. S. Jordan's Guide to the Study of Fishes, only profess to give definitions of the families with enumerations of the principal genera. Giinther's Catalogue of the Fishes in the British Museum therefore remains the only general descriptive treatise, but its last volume dates from 1870, and the work is practically obsolete. A second edition of it was begun in 1894, but only one volume, by Boulenger, has appeared, and the subject is so vast that it seems doubtful now whether any one will ever have the time and energy to repeat Giinther's achievement. The fish fauna of the different parts of the world will have to be dealt with separately, and it is in this direction that descriptive ichthyology is most likely to progress.

North America, the fishes of which were imperfectly known in 1880, now possesses a Descriptive Catalogue in 4 stout volumes, by D, S. Jordan and B. W. Evermann, replacing the synopsis brought out in 1882 by D. S. Jordan and C. H. Gilbert. A similar treatise should embrace all the fresh-water species of Africa, the fishes of the two principal river systems, the Nile and the Congo, having recently been worked out by G. A. Boulenger. Japanese ichthyology has been taken in hand by D. S. Jordan and his pupils.

The fishes of the deep sea have been the subject of extensive monographs by L. Vaillant (Travailleur and Talisman ), A. Gunther (Challenger ), A. Alcock (Investigator ), R. Collett (Hirondelle ), S. Garman (Albatross ) and a general resume up to 1895 was provided in G. B. Goode's and T. H. Bean's Oceanic Ichthyology. More than 600 true bathybial fishes are known from depths of 1000 fathoms and more, and a great deal of evidence has been accumulated to show the general transition of the surface fauna into the bathybial.

A recent departure has been the exploration of the Antarctic fauna. Three general reports, on the results of the Southern Cross, the Belgica and the Swedish South Polar expeditions, had already been published in 1907, and others on the Scotia and Discovery were in preparation. No very striking new types of fishes have been discovered, but the results obtained are sufficient to entirely disprove the theory of bipolarity which some naturalists had advocated. Much has been done towards ascertaining the life-histories of the fishes of economic importance, both in Europe and in North America, and our knowledge of the larval and post-larval forms has made great progress.

Wonderful activity has been displayed in the field of palaeontology, and the careful working out of the morphology of the archaic types has led to a better understanding of the general lines of evolution; but it is to be regretted that very little light on the relationships of the living groups of Teleosteans has been thrown by the discoveries of palaeontologists.

Among the most remarkable additions made in recent years, the work of R. H. Traquair on the problematic fishes Palaeospondylus, Thelodus, Drepanaspis, Lanarkia, Ateleaspis, Birkenia and Lanasius, ranks foremost; next to it must be placed the researches of A. S. Woodward and Bashford Dean on the primitive shark Cladoselache, and of the same authors, J. S. Newberry, C. R. Eastman, E. W. Claypole and L. Hussakof, on the Arthrodira, a group the affinities of which have been much discussed.

[ANATOMY

Authorities

- The following selection from the extremely extensive ichthyological literature which has appeared during the period1880-1906will supplement the bibliographical notice appended to section I. I. The General Subject: A. Gunther, Introduction to the Study of Fishes (Edinburgh, 1880); B. Dean, Fishes Living and Fossil (New York, 1895); T. W. Bridge and G. A. Boulenger, " Fishes," Cambridge Natural History, vii. (1904); D. S. Jordan, Guide to the Study of Fishes (2 vols., New York, 1905). II. Palaeontological: A. Fritsch, Fauna der Gaskohle and der Kalksteine der Perm- f ormation Bohmens (vols. i.-iii., Prague, 1879-1894); K. A. von Zittel, Handbuch der Palaeontologie, vol. iii. (Munich, 1887); A. Smith Woodward, Catalogue of Fossil Fishes in the British Museum, vols. i.-iii. (London, 1889-1895); A. Smith Woodward, Outlines of Vertebrate Paleiontology for Students of Zoology (Cambridge, 1898); J. S. Newberry, " The Palaeozoic Fishes of North America," Mon. U.S. Geol. Surv. vol. xvi. (1889); J. V. Rohon, " Die obersilurischen Fische von Oosel, Thyestidae and Tremataspidae," Ac. Imp. Sc. St-Petersb. xxxviii. (1892); 0. Jaekel, Die Selachier von Bolca, ein Beitrag zur Morphogenie der Wirbeltiere (Berlin, 1894); B. Dean, " Contributions to the Morphology of Cladoselache," Journ. Morphol. ix. (1894); R. H. Traquair, " The Asterolepidae," Mon. Palaeont. Soc. (1894-1904, in progress); " Report on Fossil Fishes collected by the Geological Survey of Scotland in the Silurian Rocks of the South of Scotland," Trans. Roy Soc. Edin. xxxix. (1899); L. Dollo, " Sur la phylogbnie des Digneustes," Bull. Soc. Beige Geol. vol. ix. (1895); E. W. Claypole, " The Ancestry of the Upper Devonian Placoderms of Ohio," Amer. Geol. xvii. (1896); B. Dean, " Palaeontological Notes," Mem. N. Y. Ac. ii. (190t); A. Stewart and S. W. Williston, " Cretaceous Fishes of Kansas," Univ. Geol. Surv. Kansas, vi. (Topeka, 1901); A. S. Woodward, " Fossil Fishes of the English Chalk," Palaeontogr. Soc. (1902-1903, etc.); R. H. Traquair, " The Lower Devonian Fishes of Gemunden," Roy. Soc. Edin. Trans. 40 (1903); W. J. and I. B. J. Sollas, " Account of the Devonian Fish Palaeospondylus," Phil. Trans. 196 (1903); C. T. Regan, " Phylogeny of the Teleostomi," Ann. & Mag. N.H. (7) 13 0904); C. R. Eastman, " Fishes of Monte Bolca," Bull. Mus. C.Z. 46 (1904); " Structure and Relations of Mylostoma," Op. cit. 2 (1906); 0. Abel, " Fossile Flugfische," Jahrb. Geol. Reichsanst. 56 (Wien, 1906); L. Hussakof. " Studies on the Arthrodira," Mem. Amer. Mus. N.H. ix. (1906). III. Faunistic (recent fishes): (A) Europe: E. Bade, Die mitteleuropciischen Siisswasserfische (2 vols., Berlin, 1901-1902). Great Britain: F. Day, The Fishes of Great Britain and Ireland (2 vols., London, 1880-1884); J. T. Cunningham, The Natural History of the Marketable Marine Fishes of the British Islands (London, 1896); W. C. M`Intosh and A. T. Masterman, The Life-Histories of the British Marine FoodFishes (London, 1897); Sir H. Maxwell, British Fresh-water Fish (London, 1904); F. G. Aflalo, British Salt-water Fish (London, 1904). Numerous important researches into the development, life-conditions and distributions, carried out at the Biological Laboratories at Plymouth and St Andrews and during the survey of the fishing grounds of Ireland, have been published by W. L. Calderwood; J. T. Cunningham, E. W. L. Holt, W. C. M`Intosh, J. W. Fulton, W. Garstang and Prince in the Journ. Mar. Biolog. Assoc., The Reports of the Fishery Board of Scotland, Scient. Trans. R. Dublin Soc. and other periodicals. (B) Denmark And Scandinavia: W. Lilljeborg, Sveriges och Norges Fiskar (3 vols., Upsala, 1881-1891); F. A. Smith, A History of Scandinavian Fishes by B. Fries, C. U. Ekstrom and C.Sundevall, with Plates by W. von Wright (second edition, revised and completed by F. A. S., Stockholm, 1892); A. Stuxberg, Sveriges och Norges Fiskar (Goteborg, 1895); C. G. J. Petersen, Report of the Danish Biological Station (Copenhagen, 1802-1900) (annual reports containing much information on fishes of and fishing in the Danish seas). (C) Finland: G. Sundman and A. J. Mela, Finland's Fiskar (Helsingfors, 1883-1891). (D) Germany: K. Mobius and F. Heincke, " Die Fische der Ostsee," Bericht Commiss. Untersuch. deutsch. Meere (Kiel, 1883); F. Heincke, E. Ehrenbaum and G. Duncker have published their investigations into the lifehistory and development of the fishes of Heligoland in Wissenschaftl. Meeresuntersuchungen (Kiel and Leipzig, 1894-1899); (E) Switzerland: V. Fatio, Faune des vertebras de la Suisse: Poissons (2 vols., Geneva and Basel, 1882-1890). (F) France: E. Moreau, Histoire naturelle des poissons de la France (3 vols., Paris, 1881); Supplement (Paris, 1891). (G) Pyrenean Peninsula: D. Carlos de Braganca, Resultados das investiga40es scientificas feitas a bordo do yacht "Amelia." Pescas maritimas, i. and ii. (Lisbon, 1899-1904). (H) Italy And Mediterranean: P. Doderlein, Manuale ittiologico del Mediterraneo (Palermo, 1881-1891, not completed; interrupted by the death of the author); E. W. L. Holt, " Recherches sur la reproduction des poissons osseux, principalement dans le golfe de Marseille," Ann. Mus. Mars. v. (Marseilles, 1899); (I) Western And Central Asia: L. Lortet, " Poissons et reptiles du lac de Tiberiade," Arch. Mus. d'Hist. Nat. Lyon, iii. (1883); S. Herzenstein, Wissenschaftliche Resultate der von N. M. Przewalski nach Central Asien unternommenen Reisen: Fische (St Petersburg, 1888-1891); L. Berg, Fishes of Turkestan (Russian text, St Petersburg, 1905); G. Radde, S. Kamensky and F. F. Kawraisky have worked out the Cyprinids and Salmonids of the Caucasus (Tiflis, 1896-1899). (J) Japan: F. Steindachner and L. Doderlein, " Beitrage zur Kenntniss der Fische Japans," Denkschr. Ak. Wien, (vols. 67 and 68, 1883); K. Otaki, T. Fu j ita and T. Higurashi, Fishes of Japan (in Japanese) (Tokyo, 1903, in progress). Numerous papers by D. S. Jordan, in collaboration with J. O. Snyder, E. C. Starks, H. W. Fowler and N. Sindo. (K) East Indies: F. Day, The Fauna of British India: Fishes (2 vols., London, 1889) (chiefly an abridgment of the author's Fishes of India); M. Weber, " Die Susswasserfische des Indischen Archipels," Zool. Ergebnisse e. Reise Niederl. Ostind. iii. (Leiden, 1894). Numerous contributions to the fauna of the Malay Peninsula and Archipelago by G. A. Boulenger, L. Vaillant, F. Steindachner, G. Duncker, W. Volz and C. L. Popta. (L) Africa: G. A. Boulenger, Materiaux pour la faune du Congo: poissons nouveaux (Brussels, 1898-1902, in progress); and Poissons du bassin du Congo (Brussels, 1901); G. Pfeffer, Die Thierwelt Ostafrikas: Fische (Berlin, 1896); A. Gunther, G. A. Boulenger, G. Pfeffer, F. Steindachner, D. Vinciguerra, J. Pellegrin and E. Lonnberg have published numerous contributions to the fish-fauna of tropical Africa in various periodicals. The marine fishes of South Africa have received special attention on the part of J. D. F. Gilchrist, Marine Investigations in South Africa, i. and ii. (1898-1904), and new species have been described by G. A. Boulenger and C. T. Regan. (M) North America: D. S. Jordan and B. W. Evermann, The Fishes of North and Middle America (4 vols., Washington, 1896-1900); D. S. Jordan and B. W. Evermann, American Food and Game Fishes (New York, 1902); D. S. Jordan and C. H. Gilbert " The Fishes of Bering Sea," in Fur-Seals and Fur-Seal Islands (Washington, 1899); The U.S. Bureau of Fisheries (since 1903) has published annually a Report and a Bulletin, containing a vast amount of information on North American fishes and every subject having a bearing on the fisheries of the United States; S. E. Meek, " Fresh-water Fishes of Mexico," Field Columb. Mus. Zool. V. (1904). (N) South America: C. H. and R. S. Eigenmann, " A Catalogue of the Fresh-water Fishes of South America," Proc. U.S. Nat. Mus. 14 (Washington, 1891); the same authors, F. Steindachner, G. A. Boulenger, C. Berg and C. T. Regan have published contributions in periodicals on this fauna. (0) AusTRALIA: J. E. Tenison-Woods, Fish and Fisheries of New South Wales (Sydney, 1882); J. Douglas Ogilby, Edible Fishes and Crustaceans of New South Wales (Sydney, 1893); J. Douglas Ogilby and E. R. Waite are authors of numerous papers on Australian fishes in Proc. Linn. Soc. N.S. Wales and Rec. Austral. Mus. (P) South Pacific: D. S. Jordan and B. W. Evermann, " Shore Fishes of the Hawaiian Islands," Bull. U.S. Fish. Comm. 23 (1905). (Q) Madagascar: H. E. Sauvage, Histoire physique, naturelle et politique de Madagascar, par A. Grandidier, xvi.; Poissons (Paris, 1891). (R) Oceanic Fishes: G. B. Goode and T. H. Bean, Oceanic Ichthyology (Washington, 1895); A. Gunther, Deep-sea Fishes of the " Challenger " Expedition (London, 1887); C. H. Gilbert, " Deep-sea Fishes of the Hawaiian Islands," Bull. U.S. Fish. Comm. 23 (1905); R. Collett, Norske Nordha y s Expedition: Fiske (Christiania, 1880); C. F. Lutken, Dijmphna-Togtets Zoologisk-botaniske Udbytte: KaraHavets Fiske (Copenhagen, 1886); L. Vaillant, Expeditions scientifiques du "Travailleur" et du "Talisman": Poissons (Paris, 1888); A. Agassiz, Three Cruises of the U.S. Coast and Geodetic Survey Steamer " Blake" (Boston and New York, 1888); A. Alcock, Illustrations of the Zoology of H.M.S. " Investigator": Fishes (Calcutta, 1892-1899, in progress); A. Alcock, Descriptive Catalogue of the Indian Deep-sea Fishes in the Indian Museum (Calcutta, 1899, contains references to all the previous papers of the author on the subject); R. Collett, Resultats des campagnes scientifiques accomplies par Albert I er prince de Monaco: poissons provenant des campagnes du yacht " l'Hirondelle," (Monaco, 1896); R. Koehler, Resultats scientifiques de la campagne du " Caudan," (Paris, 1896); C. H. Gilbert and F. Cramer, " Report on the Fishes dredged in Deep Water near the Hawaiian Islands," Proc. U.S. Nat. Mus. xix. (Washington, 1896); C. Lutken, " Spolia Atlantica," Vidensk. Selsk. Skr. vii. and ix. (Copenhagen, 1892-1898); C. Lutken, Danish Ingolf Expedition, ii.: Ichthyological Results (Copenhagen, 1898); S. Garman, " Reports on an Exploration off the West Coast of Mexico, Central and South America, and off the Galapagos Islands in charge 01 Alexander Agassiz, by the U.S. Fish Commission Steamer "Albatross," during 1891," Mem. Mus. Comp. Zool. vol. xxiv. (Cambridge, U.S.A., 1899). (S) Antarctic Fishes: G. A. Boulenger, Report on the Collections made during the voyage of the " Southern Cross ": Fishes (London, 1902); L. Dollo, Expedition Antarctique Beige (S.Y. " Belgica "). Poissons (Antwerp, 1904); E. Lonnberg, Swedish South Polar Expedition: Fishes (Stockholm, 1905); G. A. Boulenger, Fishes of the " Discovery" Antarctic Expedition (London, 1906).

(G. A. B.) III. Definition Of The Class Pisces. ITS Principal Divisions Fishes, constituting the class Pisces, may be defined as Craniate Vertebrata, or Chordata, in which the anterior portion of the central nervous system is expanded into a brain surrounded by an unsegmented portion of the axial skeleton; which are provided with a heart, breathing through gills; and in which the limbs, if present, are in the form of fins, as opposed to the pentadactyle, structure common to the other Vertebrata. With the exception of a few forms in which lungs are present in addition to the gills, thus enabling the animal to breathe atmospheric air for more or less considerable periods (Dipneusti), all fishes are aquatic throughout their existence.

In addition to the paired limbs, median fins are usually present, consisting of dermal rays borne by endoskeletal supports, which in the more primitive forms are strikingly similar in structure to the paired fins that are assumed to have arisen from the breaking up of a lateral fold similar to the vertical folds out of which the dorsal, anal and caudal fins have been evolved. The body is naked, or scaly, or covered with bony shields or hard spines.

Leaving aside the Ostracophori, which are dealt with in a separate article, the fishes may be divided into three subclasses: I. Cyclostomi or Marsipobranchii, with the skull imperfectly developed, without jaws, with a single nasal aperture, without paired fins, and with an unpaired fin without dermal rays. Lampreys and hag-fishes.

II. Selachii or Chondropterygii, with the skull well developed but without membrane bones, with paired nasal apertures, with median and paired fins, the ventrals bearing prehensile organs (claspers) in the males. Sharks, skates and chimaeras.

III. Teleostomi, with the skull well developed and with membrane bones, with paired nasal apertures, primarily with median and paired fins, including all other fishes. (G. A. B.) IV. Anatomy The special importance of a study of the anatomy of fishes lies in the fact that fishes are on the whole undoubtedly the most archaic of existing craniates, and it is therefore to them especially that we must look for evidence as to the evolutionary history of morphological features occurring in the higher groups of vertebrates.

In making a general survey of the morphology of fishes it is essential to take into consideration the structure of the young developing individual (embryology) as well as that of the adult (comparative anatomy in the narrow sense). Palaeontology is practically dumb excepting as regards external form and skeletal features, and even of these our knowledge must for long be in a hopelessly imperfect state. While it is of the utmost importance to pay due attention to embryological data it is equally important to consider them critically and in conjunction with broad morphological considerations. Taken by themselves they are apt to be extremely misleading.

External Features

The external features of a typical fish are intimately associated with its mode of life. Its shape is more or less that of a spindle; its surface is covered with a highly glandular epidermis, which is constantly producing lubricating mucus through the agency of which skin-friction is reduced to an extraordinary degree; and finally it possesses a set of remarkable propelling organs or fins.

The exact shape varies greatly from the typical spindle shape with variations in the mode of life; e.g. bottom-living fishes may be much flattened from above downwards as in the rays, or from side to side in the Pleuronectids such as flounder, plaice or sole, or the shape may be much elongated as in the eels.

Head, Trunk and Tail

In the body of the fish we may recognize the three main subdivisions of the body - head, trunk and tail - as in the higher vertebrates, but there is no definite narrowing of the anterior region to form a neck such as occurs in the higher groups, though a suspicion of such a narrowing occurs in the young Lepidosiren. 1 For general anatomy of fishes, see T. W. Bridge, Cambridge Natural History, and R. Wiedersheim, Vergl. Anat. der Wirbelthiere. The latter contains an excellent bibliography.

The tail, or postanal region, is probably a secondary development - a prolongation of the hinder end of the body for motor purposes. This is indicated by the fact that it frequently develops late in ontogeny.

The vertebrate, in correlation perhaps with its extreme cephalization, develops from before backwards (except the alimentary canal, which develops more en bloc ), there remaining at the hind end for a prolonged period a mass of undifferentiated embryonic tissue from the anterior side of which the definitive tissues are constantly being developed. After development has reached the level of the anus it still continues backwards and the tail region is formed, showing a continuation of the same tissues as in front, notochord, nerve cord, gut, myotomes. Of these the (postanal) gut soon undergoes atrophy.

Fins

The fins are extensions of the body surface which serve for propulsion. To give the necessary rigidity they are provided with special skeletal elements, while to give mobility they are provided with special muscles. These muscles, like the other voluntary muscles of the body, are derived from the primitive myotomes and are therefore segmental in origin. The fins are divisible into two main categories - the median or unpaired fins and the paired fins.

The median fins are to be regarded as the more primitive. The fundamental structure of the vertebrate, with its median FIG. i. - Heterocercal Tail of Acipenser. a, Modified median scales (" fulcra "); b, bony plates.

skeletal axis and its great muscular mass divided into segments along each side of the body, indicates that its primitive method of movement was by waves of lateral flexure, as seen in an Amphioxus, a cyclostome or an eel. The system of median fins consists in the first instance of a continuous fin-fold extending round the posterior end of the body - as persists even in the adult in the existing Dipneusti. A continuous median fin-fold occurs also in various Teleosts (many deep-sea Teleosts, eels, From Cambridge Natural History, vol. vii., " Fishes, &c.," by permission of Messrs. Macmillan & Co., Ltd.

FIG. 2. - Cladoselache. (After Dean.) &c.), though the highly specialized features in other respects make it probable that we have here to do with a secondary return to a condition like the primitive one. In the process of segmentation of the originally continuous fin-fold we notice first of all a separation of and an increase in size of that portion of the fin which from its position at the tip of the tail region is in the most advantageous position for producing movements of the body. There is thus formed the caudal fin. In this region there is a greatly increased size of the fin-fold - both dorsally and ventrally. There is further developed a highly characteristic asymmetry. In the original symmetrical or protocercal (= diphycercal ) type of tail (as seen in a cyclostome, a Dipnoan and in most fish embryos) the skeletal axis of the body runs straight out to its tip - the tail fold being equally developed above and below the axis. In the highly developed caudal fin of the majority of fishes, however, the fin-fold is developed to a much greater extent on the ventral side, and correlated with this the skeletal axis is turned upwards as in the heterocercal tail of sharks and sturgeons. The highest stage in this evolution of the caudal fin is seen in the Teleostean fishes, where the ventral tail-fold becomes developed to such an extent as to produce a secondarily symmetrical appearance ( homocercal tail, fig. 4).

The sharks have been referred to as possessing heterocercal tails, but, though this is true of the majority, within the limits of the group all three types of tail-fin occur, from the protocercal tail of the fossil Pleuracanthids and the living Chlamydoselachus to the highly developed, practically homocercal tail of the ancient Cladoselache (fig. 2).

The praecaudal portion of the fin-fold on the dorsal side of the body becomes broken into numerous finlets in living Crossopterygians, while in other fishes it disappears throughout part of its length, leaving only one, two or three enlarged portions - the dorsal fins (fig. 4, d.f.). Similarly the praecaudal part of the fin-fold ventrally becomes reduced to a single anal fin (a.f.), occasionally continued backwards by a series of finlets ( Scombridae). In the sucker-fishes ( Remora, Echeneis ) the anterior dorsal fin is metamorphosed into a sucker by which the creature attaches itself to larger fishes, turtles, &c.

The paired fins - though more recent developments than the median - a

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Bibliography Information
Chisholm, Hugh, General Editor. Entry for 'Ichneumon-Fly'. 1911 Encyclopedia Britanica. https://www.studylight.org/encyclopedias/eng/bri/i/ichneumon-fly.html. 1910.

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