20 



COPE 



This is the heterocercal tail (Fig. 4, B, G, and D). In later 

 forms the hsemal spines grow larger and the neural spine's 

 smaller, and the axis grows shorter by the abortion of the 

 terminal centra. As a result, the lobes of the caudal fin 

 become equal. In the most fully developed types the haemal 

 spines fuse into a fan-shaped bone which supports the fin.. 

 This is the homocercal caudal fin (Fig. 3, E). In its growth 

 it generally passes through the diphycercal and heterocercali 

 stages before reaching maturity. 



