222 FOOT-NOTES TO EVOLUTION. 



Going through the various groups of non-migratory 

 marine fishes we find that such relations are common. 

 In almost every group the number of vertebrae grows 

 smaller as we approach the equator, and grows larger 

 again as we pass into southern latitudes. 



It would be tedious to show this here by statistical 

 tables, but the value of generalization in science de- 

 pends on such evidence. This proof I have elsewhere* 

 given in detail. Suffice it to say that, taking an average 

 netful of fishes of different kinds at different places 

 along the coast, the variation would be evident. At 

 Point Barrow or Cape Farewell or North Cape a seine- 

 ful 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 Mazatlan or Pensacola or Naples, twenty-eight; and 

 at Panama or Havana or Sierra Leone, twenty-five. 

 Under the equator the usual number of vertebrae in 

 shore fishes is twenty-four. Outside the tropics this 

 number is the exception. North of Cape Cod it is virtu- 

 ally unknown. 



The next question which arises is whether we can 

 find other conditions that may affect these numbers. 

 These readily appear. Fresh-water fishes 

 Fewest vertebra ^^^,^ -^^ general more vertebrae than salt- 

 in shore fishes of r ^ c ^ -r-. 

 , . water fishes of the same group. Deep- 

 sea fishes have more vertebrae than fishes 

 of shallow waters. Pelagic fishes and free-swimming 

 fishes have more than those which live along the shores, 



* In a more technical paper on this subject entitled Relations 

 of Temperature to Vertebrae among Fishes, published in the Pro- 

 ceedings of the United States National Museum for 1891, pp. 107- 

 120. Still fuller details are given in a paper contained in the 

 Wilder Quarter-Century Book, 1893. 



