25^ 



HARDWICKE'S SCIENCE-GOSSIP. 



worms and the Eri-antia generally), and those which 

 adopt a fixed existence. The latter have no hard parts 

 to leave behind them when they die, except their horny 

 jaws, and these (as will be seen shortly) have l^een 

 found by Dr. Hind in considerable quantities in the 



favour of those tracks being of annelid origin. The 

 other class of sea-worms adopting a settled marine 

 life, live in tubes, which are formed of grains of sand, 

 etc., cemented together, as in the instance of our 

 modern Tercbdla, or they may be leathery, as in the 



Fig. 1 80.— Worm-tracks on Flags in'Quarries near Kirby-Lonsdale, Yorkshire. Lower Carboniferous formation, i natural : 





Fig. 181.— Tube of Terehella, formed of cemented sand-grains. 



Silurian and other rocks. Until a few years ago we 

 were entirely indebted for proofs of the former 

 existence of this class of sea-worms for the tracks they 

 had left behind them on the primeval mud flats, and 

 the discovery of their jaws is additional evidence in 



Fig. 182. — Coriaceous tube oi Sabella unispira (recent . 



recent Sahella ; or their outer skin may secrete lime, 

 and thus form a solid tube, as illustrated by the empty 

 tubes we see attached to old oyster shells, stones, and 

 rocks. In both the latter cases the breathing organs 

 are gathered into one place, and form a beautiful' 



