346 THE POPULAR SCIENCE MONTHLY. 



LATITUDE AND VERTEBRA. 



A STUDY IN THE EVOLUTION OF FISHES. 

 Br DAVID STARE JORDAN. 



IN this paj^er is given an account of a curious biological problem 

 and of the progress which has been made toward its solution. 

 The discussion may have a certain popular interest from the fact 

 that it is a type of many problems in the structure and distribu- 

 tion of animals and plants which seem to be associated with the 

 laws of evolution. In the light of these laws they may be more 

 or less perfectly solved. On any other hypothesis than that of 

 organic evolution the solution of the present problem, for exam- 

 ple, would be impossible. On the hypothesis of special creation a 

 solution would be not only impossible but inconceivable. 



It has been known for some years that in several groups of 

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

 species which inhabit northern waters have more vertebrae than 

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

 have sixty vertebrae ; 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 nonmigratory marine 

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

 group the number of vertebrte grows smaller as we approach the 

 equator, and grows larger again as we pass into southern latitudes. 



It would be tedious to try to prove this here by statistical 

 tables, but the value of generalization in science depends on such 

 evidence. This proof I have elsewhere * given in detail. Suffice 

 it to say that, taking an average netful of fishes of diff^erent kinds 

 at different places along the coast, the variation would be evident. 

 At Point Barrow or Cape Farewell or North Cape a seineful of 

 fishes would perhaps average eighty vertebrae apiece, the body 

 lengthened to make room for them ; at Sitka or St. Johns or Ber- 

 gen, perhaps, sixty vertebrre ; 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 vertebra^ in shore fishes is 



* In a more technical paper on this subject entitled Relations of Temperature to Yerte- 

 bric among Fishes, published in the Proceedings of the United States National Museum foi' 

 1891, pp. 107-120. Still fuller details are given in a i)aper contained in the Wilder Quar- 

 ter-Centnrv Hook, 189;j. 



