Morphology of the Fins 



'3 



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. — Cortjphwnoides 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 »fpmis_of dip Uyx^ercal tail may 

 be produced by degeneration ofT;he heterocerca/ tail, as suggested 

 ty Dr. Dollo and Dr. Boulenger, who divide dij_hycereal tails 

 into primitive and secondary. 



The peculiar tapering tail of 

 the cod, the vertebras 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. 



The term leptocercal has been 

 suggested by Gaudry, 1883, 

 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 MacrfJtridcc, 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, 



Fig. 67. — Heterocercal tail of Young 

 Trout, Salmo fnrio (Linnteus). (After 

 Parlier and Haswell.) 



