5 56 POPULAR SCIENCE MONTHLY. 



THE EVOLUTION OF FISHES. 



By President DAVID STARR JORDAN, 



LELAND STANFORD JUNIOR UNIVERSITY. 



WHEN a fish dies he leaves no friends. His body is at once at- 

 tacked by hundreds of creatures ranging from the one-celled 

 protozoa and bacteria to individuals of his own species. His flesh is de- 

 voured, his bones are scattered, the gelatinous substance in them decays, 

 and the phosphate of lime is in time dissolved in the water. For 

 this reason few fishes of the millions who die each year leave any 

 trace for future preservation. At the most, a few teeth, a fin spine or 

 a bone buried in the clay might remain intact or in such condition as to 

 be recognized. 



But now and then it happens that a dead fish may fall in more fortu- 

 nate conditions. On a sea bottom of fine clay the bones, or even the 

 whole body, might be buried in such a way as to be sealed up and pro- 

 tected from total decomposition. The flesh would in any case disappear 

 and leave no mark or at the most a mere cast of its surface. But the 

 hard parts might persist, and now and then they do persist, the lime 

 unchanged or else silicified or subjected to some other form of chemical 

 substitution. Only the scales, the teeth, the bones, the spines and the 

 fin rays can be preserved in the rocks of sea or lake bottom. In a few 

 localities, as Green Eiver in Wyoming, Monte Bolca in Tuscany and 

 Mount Lebanon in Syria, with certain quarries in Scotland and litho- 

 graphic stones in Germany, many skeletons of fishes have been found, 

 pressed flat in layers of very fine rock, their structures traced as deli- 

 cately as if actually drawn on the smooth stone. Fragments preserved 

 in ruder fashion abound in the clays and even the sandstones of the 

 earliest geologic ages. In most cases, however, fossil fishes are Imown 

 from detached and scattered fragments, many of them, especially of the 

 sharks, by the teeth alone. Fishes have occurred in all ages from the 

 Silurian to the present time and no doubt the very first lived long 

 before the Silurian. 



No one can say what the earliest fishes were like, nor do we know 

 what was their real relation to the worm-like forms among which men 

 have sought their presumable ancestors, nor to the Tunicates and other 

 chordate forms, not fish-like, but still degenerate relatives of the 

 primeval fish. 



From analogy we may suppose that the first fishes which ever were 

 bore some resemblance to the lancelet, for that is a fish-like creature 

 with every structure reduced to the lowest terms. But as the lancelet 



