72 HALF AN HOUR WITH SEA-WORMS. 



portion of the sands at low water. Nay, this very 

 habit was also indulged in millions of years ago, for 

 we find in the oldest rocks in Great Britain, the 

 Cambrian, strata ripple-marked and otherwise 

 evidencing their shallow-water origin, which are 

 thickly strewn over with the fossil castings of 

 Arencolites. 



Sea-worms are separated by naturalists into two 

 great groups, Tubicola and Errantia. The former, 

 as the name implies, inhabit tubes, some of which, 

 as in the case of the Serpulte, are formed of carbonate 

 of lime, which is a genuine secretion from the body. 

 Others exude a gummy substance, to which grains of 

 sand and fragments of shells adhere, and strengthen 

 it. The only healthy movement possessed by these 

 creatures is that of moving a little up and down their 

 Fig. si. tubes. Our readers 



cannot fail to have 

 been struck with the 

 marvellous abundance 

 of one of these genera 

 of sea- worms, the Ser- 

 pula, Fig. 31. You 

 Sea- worm. ma y gee them thickly 



clustering, in every degree of curve and coil, over 

 the backs of oyster-shells, or the surfaces of stones 

 which lie close to the low water "mark. Well does 

 this common species deserve the name given it of 

 Serpula contortuplicala. But to see it in its beauty 

 is a difficult task, and only to be fully enjoyed when 



