CHAPTER IV. 



CLASS PISCES.* 



Aquatic vertebrata which breathe by means of pharyngeal gills 

 and possess typically two pairs of appendages which never present 

 any trace of a pentadactyle structure. Median fins supported, except 

 in Marsipobranchs, by dermal fin-rays (dermotrichia) are always 

 present. There are ten pairs of cranial nerves and paired posterior 

 cardinal veins. 



Fishes are sharply marked off from all the other classes of 

 Vertebrata by the form of their pectoral and pelvic appendages. 

 These, which must be regarded as homologous with the limbs 

 of the higher groups, are cutaneous expansions supported by 

 skeletal structures, which, though presenting in their fan-like 

 arrangement some distant resemblance to the skeletal structures 

 of the pentadactyle limb, are yet never arranged on the penta- 



* Lacepede, Histoire naturelle des Poissons, 6 vols. r Paris, 1798-1803. 

 G. Ouvier et Valenciennes, Histoire naturelle des Poissons, 22 vols., 

 Paris, 1828-1849. Baer, Entwickelungsgeschichte der Fische, Leipzig, 

 1835. J. Miiller, Vergleichende Anatomie der Myxinoiden, Berlin, 1835- 

 45. Id. Ueber den Bau u. die Grenzen der Ganoiden u. d. natiirliche 

 System der Fische, Abh. d. Berlin, Akad, 1846. L. Agassiz, Recherche* 

 sur les Poissons fossiles, 5 vols. Neuchatel, 1833-44. Stannius, op. 

 cit. Heckel and Kner, Die Susswasserfische von der osterreischischen 

 Monarchic, Leipzig, 1858. A Dumeril, Ichthyologie, etc., 2 vols., Paris, 

 1866. Siebold, Die Susswasserfische von Mitteleuropa, Leipzig, 1863. 

 Blanchard, Les Poissons des eaux douces de la France, Paris, 1866. Cope, 

 " Classification of Fishes," Trans. Amer. Phil. Soc., 1870, and Proc. 

 Amer. Ass. for Adv. of Science, 1871. A. Gunther, Introduction to the Study 

 of Fishes, Edinburgh, 1880; and Catalogue of Fishes in the British 

 Museum, vols. i-viii., 1859-1870. A. S. Woodward, Catalogue of Fossil 

 Fishes in the British Museum, 3 vols. London, 1889-95. F. Day, The 

 Fishes of Great Britain and Ireland, London, 1881-83. Jordan and Ever- 

 man, Fishes of North and Middle America, Bull. U. S. National 

 Museum, no. 47, Pts. 1-4, 1896-1900. T. W. Bridge, Fishes in the Cam- 

 bridge Natural History, 1904. G. A. Boulenger, Poissons du Bassin du 

 Congo, 1901. 



