THE PHYLUM ANNELIDA 



found in many parts of the world, even on isolated oceanic islands, wherever 

 the ground is moist and the temperature sufficiently high. Locomotion is 

 effected by extension and retraction of the body, aided by the setae. These 

 bristles, presumablv homologous with certain of the polychaete setae, can be 

 withdrawn to reduce friction or protruded to catch against any surface with 

 which the worm mav be in contact. As the worm crawls, the movements of 

 the setae in each region are coordinated with the movements of the body as 

 a whole. 



Earthworms burrow in the ground from a few inches to several feet beneath 

 the surface. The burrows usually run straight down for several inches and 

 then wind about irregularly, sometimes reaching a depth of 7 or 8 feet. In 

 loose soil the worm burrows bv forcing the pointed anterior end between the 

 particles of earth. In soil of normal consistency the worm excavates the bur- 

 row by literally eating its way. The earth thus passed through the diges- 

 tive tract of the worm is deposited on the surface of the ground as the 

 feces, or castings, which are often seen in small piles where earthworms are 

 abundant. In this manner lower layers of the soil are brought to the surface, 



Fig. 14.5. An earthworm, Lumbricus lerrestns, in a nocturnal exploration of the surface near 

 its burrow. The anteroposterior differentiation in the bodv of the worm, and the specialized 

 glandular region called the clitellum, are clearly shown (cf. Fig. 14.6). (Photograph courtesy 

 The Missouri Conservationist.) 



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