LIFE 



439 



is that these should have succeeded, so far as they did, in 

 impn-ssing tln-m selves on the composite result, and in giving tone 

 to the whole. It is more natural to expect an antiquated fauna to 

 be overwhelmed by a younger and more progressive one. 



ig. 382. Cladosdache fylcri Newb. Restoration by Dean. About 1/5 

 natural size. From Cleveland Shales, Ohio. 



With the close of the Mississippian period, the chief center of 

 life interest passes from the sea to the land, first to the vegetation 

 of the Coal period, and then to land vertebrates. The history 

 of the marine invertebrates will hereafter be followed with less full- 

 ness. With the introduction of fishes it had reached its great 

 adjustments, and its further history bears a close likeness to the 

 struggles and adaptations of the history already sketched. 



Evolution of fishes. Many of the ancient invertebrates were 

 fixed, and their migrations were confined to the early stages of their 

 lives; but fishes were rovers. While restrained by conditions of food, 

 temperature, etc., they were relatively independent of local condi- 

 tions. They appear to have invaded effectually the open sea for 

 the first time in the Devonian period, though at that time, marine 

 fishes seem to have been fewer than those of inland waters. But by 

 the middle of the Mississippian period, marine fishes were in un- 

 questioned supremacy, while the fresh-water forms had declined 

 notably, so far as the record shows. In the seas, the supremacy 

 of the sharks was almost uncontested. They were more abundant, 



