ANNULATA (RING-WORMS) 147 



I.' Sketch specimen, enlarging it three times. 



2. What is the significance of the name ? 



3. What general name is applied to all such teeth ? 



4. In what part of the living animal were these ? their 

 function ? 



Fig. 57. — A tube-building worm, Spirorbis borealis Daudin, belonging to the class 

 Chaetopoda, abundant upon seaweed, etc., off the New England coast. The 

 small one to the right is natural size. The middle of the enlarged three is a 

 section of the shell. 



Spirorbis (Fig. 57). Ordovician to present. 



Minute, calcareous, spiral tubes (whence the name from 

 Latin spira, spire, + orbis, circle). These tubes are cemented 

 by their fiat underside to some foreign object. 



1. Sketch a tube. 



2. How could the body of the animal within cement this to 

 some foreign object ? 



3. Could the animal leave its tube and later return to it? 



