CHAPTER VIII 



MULTICELLULAR ANIMALS: THE EARTHWORM (LUM- 



BRICUS) 



THE earthworm is an extremely common animal the world 

 over, being found buried in moist earth in practically all parts 

 of the world. There are numerous species, differing from each 

 other in minor details, but agreeing in their fundamental 

 structure. The animals vary in size from those an inch or two 

 in length, to some which are nearly a foot; and one species 

 is reported two feet in length. Earthworms are of practical 

 importance in stirring up the soil. They are constantly en- 

 gaged in bringing soil from below to the surface, and depositing 

 it at the mouths of their burrows. By this slow but constant 

 action they are of much value to agriculture, constantly renew- 

 ing the surface soil. 



ANATOMY 



Shape of Body. Examined externally, the earthworm is an 

 elongated animal, more or less cylindrical in shape, tapering, 

 however, at the two ends; Fig. 74. The head, or anterior 

 end, is more tapering than the other, the blunter one being 

 the posterior end. One side of the animal is lighter colored 

 than the other and slightly flattened, the opposite side being 

 more rounded. When the animal is in its natural position 

 on the surface of the ground, the flat side is kept undermost 

 and the rounded and darker-colored side uppermost. We thus 

 have an anterior and a posterior end, a ventral and a dorsal 

 surface, and, consequently, a right and left side to the animals. 

 The animal is, therefore, bilaterally symmetrical. 



Segments or Metameres. The body of the earthworm is 

 divided into a number of rings (Fig. 74) called segments or 

 metameres (Gr. meta = after -f meros = part). The number 

 is not constant, being greater in the older and larger animals 



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