FOSSIL WORMS. 159 



this may be but the first stage in a series of sub- 

 sequent improvements and modifications, as in the 

 grub-like larvae of the bee and beetle, or the cater- 

 pillars of the moth and butterfly. 



Just as the worm or annelid type is largely a 

 fundamental one, so is it one of the most ancient, 

 geologically speaking. In rocks, where traces of 

 neither mollusc nor zoophyte are visible, tracks of 

 ancient sea-worms have long been known. No other 

 creature can claim such a geological immortality. Not 

 even the foraminifera arc such eloquent or trustworthy 

 witnesses of the slowness with which certain deposits 

 were laid down than they. In all marine forma- 

 tions, from the Cambrian to the latest Tertiary, sea- 

 worms have left abundant proofs of their existence. 



Many of the so-called " worm or annelid tracks " 

 in Silurian rocks, such as those denominated Chon- 

 drites or Cruziana, may have been left by creeping 

 mollusca or crawling Crustacea. But in the absence 

 of the solid parts of these creatures in the fossil state, 

 it is safer to assign such tracks to worms. In deposits 

 where fossil univalves and crustaceans are actually 

 met with, such tracks may have been left by them. 

 Still, the careful student cannot but be aware, from 

 his quiet study of any low-water mud or sand-flat at 

 the present day, that for one track left of Crustacea 

 or mollusca, ten are left by sea-worms. In short, they 

 are the great track-makers, as well as sand-diggers ; 

 and we may safely give them this position without 



