CHAPTER VII 

 ANNULATA, SEGMENTED WORMS 



The Annulata or Annelids are those worms in which the elongated, 

 usually more or less cylindrical, body is externally divided into a 

 number of rings representing the internal division into a series of 

 more or less similar somites or metameres. There is usually an ex- 

 tensive ccelom and a complicated system of blood vessels. The nervous 

 system usually consists of a dorsally located brain or cerebral gan- 

 glion in the anterior region, connected around the digestive tract to a 

 ventral nerve cord which usually has a series of ganglia corresponding 

 to the somites. The excretory organs are paired nephridia, which are 

 coiled tubes, usually one pair for each somite, connecting the ccelom 

 with the exterior. 



The annelids are variously classified by different authors; the two 

 most important classes and the only two of serious economic importance 

 are the Chaetopoda, represented by the earthworms and the Hirudinea 

 or leeches. 



Earthworms. There are some 800 species of earthworms, about 90 

 of which are found in North America. There are about a dozen species 

 of the common Lumbricus and Allolobophora. There are several from 

 South Africa and Australia that are described as being iJ/ meters in 

 length. They are found everywhere except in frozen latitudes and al- 

 titudes and in dry sandy regions. They generally burrow below frost 

 in winter though some are said to survive freezing. According to the 

 operator of a large steam-shovel they are sometimes found 18 or 20 

 feet below the surface of the ground. 



They feed on almost any kind of organic matter, a considerable 

 portion of which they obtain from earth that is passed through the body. 

 This earth from which the food has been extracted is deposited at night 

 around the openings of their burrows as fine pellets known as castings. 

 The amount brought up each night by each worm is so considerable as to 



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