CHAPTER III 







ISOSPONDYLI 



! HE Subclass Teleostei, or Bony Fishes. The fishes which 

 still remain for discussion constitute the great sub- 

 class or series of Teleostei (reAeo?, true; ocrreov, bone), 

 or bony fishes. They lack wholly or partly the Ganoid traits, 

 or show them only in the embryo. The tail is slightly, if at all, 

 heterocercal ; the actinosts of the pectoral fins are few and large, 

 rarely over five in number, except among the eels; the fulcra 

 disappear; the air-bladder is no longer cellular, except in very 

 rare cases, nor does it assist in respiration. The optic nerves 

 are separate, one running to each eye without crossing; the 

 skeleton is almost entirely bony, the notochord usually dis- 

 appearing entirely with age; the valves in the arterial bulb 

 are reduced in number, and the spiral valve of the intestines 

 disappears. Traces of each of the Ganoid traits may persist 

 somewhere in some group, but as a whole we see a distinct 

 specialization and a distinct movement toward the fish type, 

 with the loss of characters distinctive of sharks, Dipnoans, and 

 Ganoids. In a general way the skeleton of all Teleosts corre- 

 sponds with that of the striped bass (see Figs 22, 23, Vol. I), and 

 the visceral anatomy is in all cases sufficiently like that of the 

 sunfish (Fig. 16, Vol. I). 



The mesocoracoid or praecoracoid arch, found in all Ganoids, 

 persists in the less specialized types of bony fishes, although 

 no trace of it is found in the perch-like forms. With all this, 

 there is developed among the bony fishes an infinite variety 

 in details of structure. For this reason the Teleostei must be 

 broken into many orders, and these orders are very different 

 in value and in degrees of distinctness, the various groups being 

 joined by numerous and puzzling intergradations. 



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