Among the morays, _Muræna helena_ has 140; _Gymnothorax meleagris_, 120; _G. undulatus_, 130; _G. moringa_, 145; _G. concolor_, 136; _Echidna catenata_, 116; _E. nebulosa_, 142; _E. zebra_, 135. In other families the true eel, _Anguilla anguilla_, has 115; the conger-eel, _Leptocephalus conger_, 156; and _Murænesox cinereus_, 154. =Variations in Fin-rays.=--In some families the number of rays in the dorsal and anal fins is dependent on the number of vertebræ. 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 vertebræ. The myotomes or muscular bands on the sides are usually coincident with the number of vertebræ. As, however, these and other characters are dependent on differences in vertebral segmentation, they bear the same relations to temperature or latitude that the vertebræ themselves sustain. Thus in the _Scorpænidæ_, _Sebastes_, and _Sebastolobus_ arctic genera have the dorsal rays xv, 13, the vertebræ 12+19. The tropical genus _Scorpæna_ has the dorsal rays xii, 10, the vertebræ 10+14, while the genus _Sebastodes_ of temperate waters has the intermediate numbers of dorsal rays xii, 12, and vertebræ 12+15. =Relation of Numbers to Conditions of Life.=--Fresh-water fishes have in general more vertebræ than marine fishes of shallow waters. Pelagic fishes and deep-sea fishes have more than those which live along the shores, and more than localized or non-migratory forms. To each of these generalizations there are occasional partial exceptions, but not such as to invalidate the rule. The presence of large numbers of vertebræ is noteworthy among those fishes which swim for long distances, as, for example, many of the mackerel family. Among such there is often found a high grade of muscular power, or even of activity, associated with a large number of vertebræ, these vertebræ being individually small and little differentiated. For long-continued muscular action of a uniform kind there would be perhaps an advantage in the low development of the vertebral column. For muscular alertness, moving short distances with great speed, the action of a fish constantly on its guard against enemies or watching for its prey, the advantage would be on the side of a few vertebræ. There is often a correlation between the free-swimming habit and slenderness and suppleness of the body, which again is often dependent on an increase in numbers of the vertebral segments. These correlations appear as a disturbing element in the problem rather than as furnishing a clew to its solution. In some groups of fresh-water fishes there is a reduction in number of vertebræ, not associated with any degree of specialization of the individual bone, but correlated with simple reduction in size of body. This is apparently a phenomenon of degeneration, a survival of dwarfs, where conditions are unfavorable in full growth.