28 David Starr Jordan 



It is evident that the two families most decidedly tropical 

 in their distribution, the morays* and the snake eels.f have 

 diverged farthest from the primitive stock. They are most 

 "degenerate," as shown by the reduction of their skeleton. 

 At the same time they are also most decidedly "eel-like," 

 and in some respects, as in coloration, dentition, muscular de- 

 velopment, most highly specialized. It is evident that the 

 presence of numerous vertebral joints is essential to the sup- 

 pleness of body which is the eel's chief source of power. 



So far as known the numbers of vertebrae in eels range from 

 115 to 225, some of the deep-sea eelsj having probably higher 

 numbers, if we can draw inferences from their slender or 

 whip-like forms ; but this character may be elusive. 



VARIATIONS IN FIN-RAYS. 



In some families the number of rays in the dorsal and anal 

 fins is dependent on the number of vertebrae. It is therefore 

 subject to the same fluctuations. § This relation is not 

 strictly proportionate, for often a variable number of rays 

 with their interspinal processes will be interposed between a 

 pair of vertebrae. The myotomes or muscular bands on the 

 sides are usually coincident with the number of vertebrae. 

 As, however, these and other characters are dependent on 

 differences in vertebral segmentation, they bear the same rela- 

 tions to temperature that the vertebrae themselves sustain. 



* Murcenidce. Among the tnorays, Mtiroena helena has 140/ 

 Gynmothorax meleagris, 120; G. undulatus, 130/ G. moringa, 145 ,• 

 G. concolor, 136; Echidna catenata, 116/ E. nebulosa, 142; E. zebra, 

 135. In other families the tme eel, Anguilla anguilla, has 115; the 

 Conger eel, Leptocephalus conger, 156 ; Murcenesox cinereus, 154 ; 

 M. coniceps, 154; Ophichthys ocellatus, 134; O. gomesi, 141 ; Syna- 

 phobranchus pinnatus, 146 ; Gordiichthys irretitus, 225. 



t Ophisuridce. 



X Nernichihys, Nettastoma, Venefica. 



I Thus in the Scorpcenidce, Sebastes, the arctic genus has the dorsal 

 rays xv, 13, the vertebrae 12 -|- 19. The tropical genera Scorpcena and 

 Sebastoplus have the dorsal rays xu, 10, the vertebrae 10 + 14, while the 

 semitropical genus Sebastodes has the intermediate numbers of dorsal 

 rays xii, 12, and vertebrae 12 -\- 15. 



