POLYCHiETA. 4^9 



the deposits in which the trails occur, as we might reasonably 

 expect to do. 



Principal Dawson, again, suggests "that Algae and also land- 

 plants, drifting with tides and currents, often make the most remark- 

 able and fantastic trails," which might easily be mistaken for the 



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m 



hk 



Fig. 351. — Track of the living Purf>7(ra lapillus on firm sand, reduced three diameters'. 

 (From a drawing made by the late Robert Gray.) 



tracks of Annelides. This suggestion is a very valuable one, but 

 certainly will not explain the origin of the majority of the so-called 

 " Annelide-tracks " of the Palaeozoic rocks, the regular serpentine 

 form of which is one of their most remarkable features. 



Lastly, some observers are disposed to see in these supposed 

 tracks and trails the remains of various forms of Algce, the drifted 



