CHAPTER XIX 



THE EARTHWORM AND OTHER SEGMENTED 

 WORMS 



Or all the animals that are called worms only a few are true 

 worms; most of them are the larvae of insects. The true worms 

 are divided into three phyla : (i) the segmented worms or Anne- 

 lida, like the earthworm ; (2) the roundworms, or Nemathel- 

 minthes, like the trichina that sometimes infests pork ; and (3) 

 flatworms, or Platyhdminthes, like the tapeworm. 



Need of Moisture. — The earthworm is the most common 

 member of the phylum Annelida, and is abundant almost every- 

 where if the soil is suitable. The skin of the earthworm is soft 

 and naked, like that of the snail or slug; it is covered with a 

 thin, slimy fluid and requires damp soil or damp atmosphere or 

 else it will dry up. For this reason earthworms are never found 

 in dry, sandy soil, and appear above ground only on dewy 

 nights (Fig. 91), or in cloudy weather, or after a rain. Earth- 

 worms are not rained down, as many people suppose, but are 

 rained up out of their burrows. 



Burrows. — The body of the earthworm is cylindrical, and 

 long and slender; it is well adapted to the animal's burrowing 

 activities, since the earth offers little resistance to its " vermi- 

 form " shape. The burrows are scarcely larger than the diam- 

 eter of the body and extend, as a rule, only for about two feet 

 underground, although burrows six feet long are sometimes dug. 



Locomotion. — In traveling within the burrow as well as 

 on the surface, and in digging the burrows, the movements of 

 the body are similar. The anterior end is extended and the 

 rest of the body drawn up to it. This is accomplished by the 

 muscles in the body wall (Fig. 96, bw). An examination of a 



168 



