Class 2. Pisces. 



359 



skeleton, is more or less completely replaced by true bone. The 

 vertebral column (Fig. 298), is not infrequently represented 





S ^ 

 Ui I- 



O c3 

 O 'o 



•5 f3 



^ S 



(S CO 



is 



T-l t-l 

 <0 



SI 



H CO _N 

 , -'So 

 c3 d « 



® o S 





■^ §"3 



o o 



(in the Cyclostomes^ some SelacliianSj Dipnoans, and cartilaginous 

 Ganoids) by a continuous tube of cartilage or connective tissue "wbich 



