454 



The Evolution of Fishes 



The Bony Fishes. — All the remaining fishes have ossified 

 instead of cartilaginous skeletons. The dipnoan and ganoid 

 traits one by one are more or less completely lost. Through 

 these the main line of fish development continues and the 

 various groups are known collectively as bony fishes or teleosts. 



The earhest of the true bony fishes or teleosts appear in Meso- 



FiG. 26.5. — A primitive Herring-like fish, Holcolepis lewesiensis Mantell, restored. 

 Family Elopidic. English Chalk. (After Woodward.) 



zoic times, the most primitive forms being soft-rayecl fishes Avith 

 the vertebrae all similar in form, allied more or less remotely 

 to the herring of to-day, but connected in an almost unbroken 

 series with the earliest ganoid forms. In these and other soft- 

 rayed fishes the pelvis still retains its posterior insertion, the 



Fig. 266.— Ten-pounder, EIops saurus L. An ally of the earliest bony fishes. 



Virginia. 



ventral fins being said to be abdominal. The next great stage 

 in evolution brings the pelvis forward, attaching it to the shoulder- 

 girdle so that the ventral fins are now thoracic as in the perch 

 and bass. If brought to a point in front of the pectoral fins, 

 a feature of speciahzed degradation, they become jugular as in 

 the codfish. In the abdominal fishes the air-bladder still re- 

 tains its rudimentary duct joining it to the oesophagus. 



From the abdominal forms allied to the herring, the huge 



