Adaptations of Fishes 2 i i 



the deep-sea forms have been counted, no conclusions can 

 be drawn as to the relation of their vertebra) to the tempera- 

 ture. 



It is evident that the two families most decidedly tropical 

 in their distribution, the morays {M ura-indcc) and the snake-eels 

 {O.phidUhyida;) , 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 

 development, 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 \'ertebr£e in eels range from 

 115 to 160, some of the deep-sea eels (Netniclithys, Nettastonia, 

 GordiicJithys) having much higher numbers, in accord with 

 their slender or whip-like forms. 



Among the morays, Miirccua Helena has 140; Gymnothorax 

 meleagris, 120; G. nndidatiis, 130; G. moringa, 145; G. concolor, 

 136; Ediidna catenata, 116; E. nebulosa, 142; E. zebra, 135. 

 In other families the true eel, Angnilla angnilla, has 115; the 

 conger-eel, Leptocephalns conger, 156; and Mnrcenesox cinerens. 



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 inter- 

 posed between a pair of vertebra;. The myotomes or muscular 

 bands on the sides are usually coincident with the number of 

 vertebra. As, however, these and other characters are de- 

 pendent on differences in vertebral segmentation, they bear 

 the same relations to temperature or latitude that the vertebra; 

 themselves sustain. 



Thus in the Scorpccmdcc, Sebastes, and Scbastolobns arctic 

 genera have the dorsal rays xv, 13, the vertebra; 12-^19- The 

 tropical genus Scorpcsna has the dorsal rays xii, 10, the ver- 

 tebra; JO +14, while the genus Sebastodes of temperate waters 

 has the intermediate numbers of dorsal rays xii, 12, and ver- 

 tebra 1 2 -f- 1 .'^ . 



