CHAPTER XIV 



EARTHWORMS, LEECHES AND OTHER SEGMENTED 



WORMS 



The segmented worms (branch Annelida, annellus, little 

 ring), of which the earthworm is the most common example, 

 show a decided advance in structure over the flat-worms and 

 round-worms. Their bodies are divided into a series of seg- 

 ments, and most of them have well developed nervous and 

 circulatory systems. There is a definite body-cavity, and 

 paired organs of excretion called nephridia. 



The segmented worms are grouped in four classes, the 

 Chatopoda (Gr. chaite, hair; pous, foot) including the earth- 

 worms and many marine worms; the Hirudinea (L. hirudo, 

 leech) or leeches; and the marine Archiannelida (Gr. arc hi-, 

 primitive; annellus, little ring) and Gephyrea (Gr. gephyrd, 

 bridge). 



The Earthworm. In the Chatopoda the sides of the body 

 are furnished with minute setae, or with special locomotor 

 protrusions known as parapodia. The familiar earth-worm, or 

 angle-worm, or fish- worm, as it is often called, will serve as an 

 example of the group. Earth-worms eat their way through the 

 ground forming definite burrows and bringing to the surface 

 soil from considerable depths. The earth that is swallowed as 

 they are digging contains more or less decaying vegetable matter 

 which is used as food. Darwin was the first to call attention to 

 the great good that the earthworms do by opening up the 

 soil so water can enter, enabling plant roots to penetrate 

 deeper, and by bringing to the surface soil from which the 

 various plant foods have not yet been taken by the plants. 

 He estimated that in England and conditions are prac- 

 tically the same in America about ten tons of soil per 

 acre pass annually through the bodies of these worms, and 



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