SILURIAN WORM TRACKS. 175 
especially on the coast of Brazil. The minute nautilus-like 
shells of Spirorbis live attached to the fronds of sea-weeds, 
especially the different kinds of Fucus. 
ZA 6 ese [WIG AL | mS 
TSN KES i x O 
Fe me Or 
pt) fi (Cale yO. 
Fig. 124.—Cirratulus grandis.—After Verrill. 
Many sea-worms are highly phosphorescent, the light emit- 
ted being intensely green. The tracks of worms like the 
Nereis of to-day occur in the lower Silurian slates; their 
bristles, however, were spinulose, as in the larval worms. 
Thus the type, though highly specialized, has, unlike most 
specialized groups, a high antiquity, the specialized Anne- 
lides existing side by side with the generalized Polyzoa and 
Brachiopoda. At the present time the Annelides are widely 
distributed in the seas of the globe, the tropical forms being 
exceedingly abundant among coral stocks and in sponges, 
while the arctic seas abound with Annelid life. They also 
sparingly exist at great depths, one species of a worm allied 
