ANNELIDA. 319 



of this nature occur abundantly in the Lower Cambrian 

 strata of the Longmynd, and are also far from uncommon 

 in deposits of Silurian age. 



II. Wandering Burrows. Various recent Annelides, among 

 which the common Lug -worm (Arenicola, piscatorum) is a 

 notable example, form long, wandering, irregular, and tortu- 

 ous tunnels in the sand of the sea-shore, at a little distance 

 below the surface. In these cases the worm subsists upon 

 particles of organic matter disseminated through the sand 

 or mud, through which, therefore, it literally eats its way. 

 The burrows thus formed are, consequently, very irregular ; 

 they principally have a horizontal direction ; if formed by 

 many individuals, they may cross or intersect one another in 

 various ways ; and as the worm proceeds on its course, they 

 become filled up in the rear of the advancing animal by the 

 sand which has been passed through the alimentary canal, 

 some of this sand being often voided at some point at the 

 surface to form the tortuous " worm-casts," with which every 

 wanderer on the sea-shore is so familiar. Bodies which we 

 may reasonably assume to be of essentially the same nature 

 as the filled up " wandering burrows " of worms like the 

 living Lug- worm, are well known to all workers amongst 

 the more ancient, muddy, and sandy strata of the earth's 

 crust, and they have received various names, and have had 

 very various origins ascribed to them. They usually present 

 themselves as irregularly cylindrical, worm-like elevations of 

 the surfaces of the strata (fig. 191), which usually are more 

 or less parallel with the laminae of deposition, but often run 

 somewhat obliquely to these, so as to thread successive laminae 

 to one another. Generally, they differ slightly in texture 

 and colour from the surrounding rock as can well be 

 supposed, if their origin be as above described and from 

 their somewhat superior hardness, they resist disintegration 

 by weathering, and thus come to stand out prominently 

 above the surface. Though they may be much matted 

 together, and may thus appear to branch, it is not probable 

 that they really subdivide. It would appear that many of 

 the fossils of the Palaeozoic rocks which have been referred 

 to the Fucoids, under the generic titles Palceochorda, Palceo- 



