21 o Adaptations of Fishes 



tion to the temperature, though it seems to be related in some 

 degree to the habits of the species. Perhaps the retention of 

 many segments is connected with that strength and swiftness 

 in the water for which the mackerels are preeminent. 



The variations in the number of vertebrae in this group led 

 Dr. Giinther to divide it into two families, the Carangida and 

 Scombridce. 



The Carangidaz or Pampanos are tropical shore fishes, local 

 or migratory to a slight degree. All these have from 24 to 

 26 vertebrae. In their pelagic relatives, the dolphins (Cory- 

 ph&na), there are from 30 to 33; in the opah (Lampris), 45 ; in 

 Brama, 42; while the great mackerel family (Scombrida) , all 

 of whose members are more or less pelagic, have from 31 to 50. 



The mackerel (Scomber scombrus) has 3 1 vertebrae ; the chub 

 mackerel (Scomber japonicus], 31 ; the tunny (Thunnus thynnus), 

 39; the long-finned albacore (Germo alalonga) , 40; the bonito 

 (Sarda sarda), 50; the Spanish mackerel (S comber omorus macu- 

 latus), 45. 



Other mackerel-like fishes are the cutlass-fishes (Trickiuridaf), 

 which approach the eels in form and in the reduction of the fins. 

 In these the vertebrae are correspondingly numerous, the num- 

 bers ranging from 100 to 160. Aphanopus has 101 vertebrae; 

 Lepidopus, 112; Trichurus, 159. 



In apparent contradiction to this rule, however, the pelagic 

 family of swordfishes (Xiphias] , remotely allied to the mackerels, 

 and with even greater powers of swimming, has the vertebrae 

 in normal number, the common swordfish having but 24. 



The Eels. The eels constitute a peculiar group of soft-rayed 

 ancestry, in which everything else has been subordinated to 

 muscularity and flexibility of body. The fins, girdles, gill- 

 arches, scales, and membrane bones are all imperfectly developed 

 or wanting. The eel is perhaps as far from the primitive stock 

 as the most highly "ichthyized" fishes, but its progress has 

 been of another character. The eel would be regarded in the 

 ordinary sense as a degenerate type, for its bony structure is 

 greatly simplified as compared with its ancestral forms, but in 

 its eel-like qualities it is, however, greatly specialized. All 

 the eels have vertebrae in great numbers. As the great majority 

 of the species are tropical, and as the vertebrae in very few of 



