Temperature and Vertebrce 19 



individuals. They abound in the depths of the ocean, but 

 there are comparatively few of them in the tropics. 



The Salmonidce * which inhabit the rivers and lakes of the 

 northern zones have from 60 to 65 vertebrae. The Scopelidee, 

 Stouiiatidce, and other deep-sea analogues have from 40 up- 

 wards to perhaps 100, in the few species in which the number 

 has been counted. In these the weakness of the skeleton and 

 the frequent disconnection of the shoulder girdle from the 

 head seem to be features of degradation. 



The group of ClupeidcB f is probably nearer the primitive 

 stock of Isospondyli than the salmon are. This group is es- 

 sentially northern in its distribution, but a considerable num- 

 ber of its members are found within the tropics. The com- 

 mon herring % ranges farther into the arctic regions than any 

 other. Its vertebrae are 56 in number. In the shad, § a 

 northern species which ascends the rivers, the same number 

 has been recorded. 



The sprat II and sardine^ ranging farther south, have 

 from 48 to 50, while in certain small herring '^* which are 

 strictly confined to tropical shores the number is but 40. 



Allied to the herring are the anchovies, mostly tropical. 

 The northernmost species, ft the common anchovy of Europe, 

 has 46 vertebrae. A similar species in the temperate Pacific 

 {Stolephorus mordax) has 44. A tropical species Xt has 41 

 segments. 



There are, however, a few soft-rayed fishes §§ confined to 

 the tropical seas in which the numbers of vertebrae are still 

 large, an exception to the general rule for which there is no 

 evident reason unless it be connected with the wide distribu- 

 tion of these almost cosmopolitan fishes, which may have had: 

 pelagic ancestors. 



* Salmon, trout, grayling, whitefish, etc. 



t Herring, shad, sprat, sardine, and their allies. 



X Clupea harengus. \ Clupea alosa, the European shad. 



II Clupea sprattus. \ Clupea pilchardus. 



** Harejigula niacrophthalma. ft Engranlis enchrasicoliis. 



%% Stolephorus browni. 



\\ Among these are Albula vulpes, the bonefish, with 70 vertebrae, 

 Elops saurus, the ten-pounder, with 72, the Grande Ecaille {Megalops) 

 with 57, and C/ianos chanos with 72. 



