Morphology of the Fins 83 



The homocercal tail is the fan-shaped or symmetrical tail 

 common among the Teleosts, or bony fishes. In its process 

 of development the individual tail is first archicercal, then 

 lophocercal, then diphycercal, then heterocercal, and lastly homo- 



FIG. 66. Coryphcenoides carapinus (Goode and Bean), showing leptocercal tail. 



Gulf Stream. 



cereal. A similar order is indicated by the sequence of fossil 

 fishes in the rocks, although some forms of diphycercal tail may 

 be produced by degeneration of the heterocercal tail, as suggested 

 by Dr. Dollo and Dr. Boulenger, who divide diphycercal tails 

 into primitive and secondary. 



The peculiar tapering tail of 

 the cod, the vertebrae growing 

 progressively smaller behind, is 

 termed isocercal by Professor 

 Cope. This form differs little 

 from diphycercal, except in its 

 supposed derivation from the 

 homocercal type. A similar 



form is seen in eels. FIG. 67. Heterocercal tail of Young 



The term leptocercal has been Trout, Salmo fario (Linnaeus). (After 



suggested by Gaudry, 1883, Parker and HasweU ' ) 

 for those tails in which the vertebral column ends in a point. 

 We may, perhaps, use it for all such as are attenuate, ending 

 in a long point or whip, as in the Macrourida, or grenadiers, 

 the sting-rays, and in various degenerate members of almost 

 every large group. 



The term gephyrocercal is devised by Ryder for fishes in 

 which the end of the vertebral axis is aborted in the adult, 

 leaving the caudal elements to be inserted on the end of this 

 axis, thus bridging over the interval between the vertical fins, 



