EARTHWORM 



345 



almost universally as a laboratory specimen. Lumbricus is not as 

 common in the Southwest as are other large forms of earthworms, 

 but is used here as an example because it is so well known and because 

 its features represent so well those common to the entire order. 



External Anatomy of the Earthworm 



The body of Lu7nhricus varies from six to fourteen inches in 

 length and gives the appearance of a series of rings joined in a 



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Fig-. 125. — External anatomy of earthworm, ventral view, segments numbered 

 in Roman numerals. (From Wolcott, Animal Biology, McGraw-Hill Book Com- 

 pany, Inc.) 



linear arrangement. The rings are the body segments, or meta- 

 meres, and vary in number up to 150. In the adult the number of 

 segments from the anterior end to the posterior end of the clitellum 



