6o RELICS OF PRIMEVAL LIFE 



at present,^ while their generally larger size in the 

 earlier formations tends to show that they have 

 rather been degenerating in the lapse of geological 

 time. 



In regard to the Sea-worms, the burrows, cast- 

 ings, and trails found in the pre-Cambrian beds are 

 scarcely, if at all, different from those now seen on 

 sandy and muddy shores, and would seem to indicate 

 that these highly organized and very sensitive and 

 active creatures swarmed in the muddy bottom of 

 the pre-Cambrian Sea, and lived in the same way 

 as at present. It is impossible, however, to know 

 anything of the internal structures of these creatures, 

 but the marks left by their bristle-bearing feet seem 

 to indicate that some of them at least belong to 

 the higher group of Sea-centipedes, creatures rival- 

 ling the Crustaceans in complexity of organization, 

 and near to them in plan of structure, though at 

 present usually widely separated from them in cur- 

 rent systems of classification. In the Ordovician 

 system, next above the Cambrian, Hinde has found 

 many curiously formed jaws of animals of this kind, 



* PalcEocypris Edwardst, Brougniart, Coal Formation of St. 

 Etienne, France. 



