The Evolution of Fishes 443 



lake bottom. In a few localities, as near Green River in Wyo- 

 ming, Monte Bolca, near Verona, and Mount Lebanon in Syria, 

 the London clays, with certain quarries in Scotland and lith(j- 

 graphic stones in Germany, many skeletons of fishes have been 

 found pressed flat in layers of very fine rock, their structures 

 traced as delicately 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 known from detached and scattered frag- 

 ments, 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 probably the very first lived long before the Silurian. 



The Earliest Fishes. — 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 has no hard parts, no bones, nor 

 teeth, nor scales, nor fins, no traces of its kind are found among 

 the fossils. If the primitive fish was like it in important respects, 

 all record of this has probably vanished from the earth. 



The Cyclostomes. — The next group of living fishes, the 

 Cyclostomes, including the hagfishes and lampreys, — fishes 

 with small skull and brain but without limbs or jaws, — stands 

 at a great distance above the lancelet in complexity of struc- 

 ture, and equally far from the true fishes in its primitive sim- 

 plicity. In fact the lamprey is farther from the true fish in 

 structure than a perch is from an eagle. Yet for all that it may 

 be an offshoot from the primitive line of fish descent. There 

 is not much in the structure of the lamprey which may be pre- 

 served in the rocks. But the cartilaginous skull, the backbone, 

 fins, and teeth might leave their traces in soft clay or hthographic 

 stone. But it is certain that they have not done so in any 

 rocks yet explored, and it may be that the few existing lampreys 

 owe their form and structure to a process of degradation from 

 a more complex and more fish-like ancestry. The supposed 



