CHAPTER XVII. 

 PHYLUM VIII: ANNULATA (OR SEGMENTED WORMS). 



213. General Survey. The segmented worms include 

 the earthworms, many minute fresh-water worms, the 

 leeches, and numerous marine worms. They are scat- 

 tered over the earth and are adapted to many manners 

 of living. They all have elongated bodies, and the great 

 majority of them burrow in the soil or sand, or swim freely 

 through the water. Some of the sea-worms, however, 

 bore into more solid objects and remain permanently 

 in their burrows, extending only the front part of the 

 body from the tubes in search of oxygen and food. These 

 occur in great numbers among the sponges and coral 

 reefs. The worms furnish food for a great many other 

 animals, and they in turn live on decaying organic matter 

 and on the minute plant and animal life that is found in 

 the waters. 



The structural qualities that make them interesting 

 to the student are as follows: 



1. They are bilaterally symmetrical and the anterior 

 end shows a more highly developed head than in any of 

 the phyla which we have yet studied. 



2. The outside of the body shows a series of rings, or 

 segments, one after another in the long axis of the body. 

 This is known as segmentation. The segments are much 

 more alike than those we studied in the crayfish (Ch. VIII) . 

 Several internal' organs are segmented also. 



3. While the outside does not show it, the internal 



195 



