GENERAL ZOOLOGY 



Prostomium 

 Mouth 



Openings of 



seminal 



receptacles 



Opening of 

 oviduct 



Opening of 

 ductus deferens 



Clitellum 



Fig. 14.6. Some external features of the anterior and posterior 

 ends of the earthworm; ventral view. (From W. T. Sedgwick 

 and E. B. Wilson, General Bioloay^ copyright 1914 by Henry 

 Holt and Co., reprinted by permission.) 



and the effect upon the soil resembles that produced by turning with a plow. 

 Earth which has passed through the worm's digestive tract is also modified 

 chemically, and thus the tunneling activities of earthworms produce a two- 

 fold benefit to the soil. 



Earthworms are nocturnal in their activities at the surface, although they 

 sometimes appear in daylight after a shower. During the day they lie in the 

 vertical part of the burrow near the surface, unless engaged in excavating 

 at a greater depth. The mouth of the burrow is often closed by bits of grass 

 or other materials drawn in at the finish of the night's activities. With the 

 onset of darkness again, this plug is pushed aside, and the worm extends the 

 anterior end of its body, exploring the surface in all directions but keeping 

 the posterior end within the burrow. If disturbed, it can retract the exposed 

 anterior end with surprising rapidity. When the soil is moist and atmospheric 

 humidity high, earthworms secure most of their food at the surface. Leaves, 

 bits of grass, and other plant materials are smeared with a saliva-like fluid 

 and, thus softened, are nibbled away by the lips and swallowed. In times of 

 drought, the worms avoid the surface and must depend on such nutrients as 

 may be extracted from the soil that passes through the digestive tract in con- 

 nection with their burrowing activities. 



External Anatomy. The elongated, cylindrical body is bluntly pointed at 

 both ends and is somewhat flattened or spatulate posteriorly (Fig. 14.6). 

 The mouth is at the anterior end, surrounded by the first somite and over- 

 hung by a fleshy protuberance, the prostomium. The anus is a vertical slit- 



404 



