Adaptations of Fishes 



203 



fishes (wrasse-fishes, flounders, and "rock-cod," for example) 

 those species which inhabit northern waters have more vertebras 

 than those living in the tropics. Certain arctic flounders, for 

 example, have sixty vertebra; tropical flounders have, on the 

 average, thirty. The significance of this fact is the problem at 

 issue. In science it is assumed that all facts have significance, 

 else they would not exist. It becomes necessary, then, to find 

 out first just what the facts are in this regard. 



Going through the various groups of non-migratory marine 

 fishes we find that such relations are common. In almost every 

 group the number of vertebrce grows smaller as we approach the 

 equator, and grows larger again as we pass into southern lati- 

 tudes. Taking an average netful of fishes of difTerent kinds 

 at different places along the coast, the variation would be evi- 

 dent. At Point Barrow or Cape Farewell or North Cape a 



Fig. 1.54. — Skeleton of Pike, Esox lucius Linnaeus, a river fish with many vertebrae. 



seineful of fishes would perhaps average eighty vertebrae each, 

 the body lengthened to make room for them; at Sitka or St. 

 Johns or Bergen, perhaps sixty vertebrae; at San Francisco or 

 New York or St. Malo, thirty-five; at JIazatlan or Pensacola or 

 Naples, twenty-eight; and at Panama or Havana or Sierra 

 Leone, twenty-five. Under the equator the usual number of 

 vertebra in shore fishes is twenty-four. Outside tropical and 

 semitropical waters this number is the exception. North of 

 Cape Cod it is virtually unknown. 



Number of Vertebrae. — The numbers of vertebnc in different 

 groups may be summarized as follows : 



Lancelets. — Among the lancelets the numbers of segments 

 range from 50 to 80, there being no vertebnc. 



Lampreys. — In this group the number of segments ranges 

 from 100 to 150. 



