| LATITUDE AND VERTEBRÆ. |
A STUDY IN THE EVOLUTION OF FISHES.
By DAVID STARR JORDAN.
IN this paper 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 distribution 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 example, 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 vertebræ than those living in the tropics. Certain arctic flounders, for example, have sixty vertebræ; 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 vertebræ 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[1] 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 seineful of fishes would perhaps average eighty vertebræ apiece, the body lengthened to make room for them; at Sitka or St. Johns or Bergen, perhaps, sixty vertebræ; 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 vertebræ in shore fishes is
- ↑ In a more technical paper on this subject entitled Relations of Temperature to Vertebræ among Fishes, published in the Proceedings 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 Hook, 1893.
