WORMS 



49 



damp earth disappeared first? What is indicated as to a 

 sense of taste ? 



Why is the bilateral type of structure better adapted for 

 development and higher organization than the radiate type 

 of the starfish ? The earthworm's body is a 

 double tube ; the hydra's body is a single 

 tube ; which plan is more advantageous, and 

 why ? Would any other colour do just as well 

 for an earthworm ? Why, or why not ? 



The sandworm (Nereis) lives in the sand of the 

 seashore, and swims in the sea at night (Fig. 79). 

 It is more advanced in structure than the earth- 

 worm, as it has a distinct head (Fig. 80), eyes, two 

 teeth, two lips, and several pairs of antennae, and 

 two rows of muscular projections which serve as 

 feet. It is much used by fishermen for bait. If 

 more easily obtained, it may be studied instead of 

 the earthworm. 



There are four classes in the branch Vermes : 



1) the worms, including sandworms and leeches; 2) the 

 roundworms, including trichina, hairworms, 

 and vinegar eels; 3) Jlatworms, including 

 tapeworm and liver fluke ; 4) rotifers, which 

 are microscopic aquatic forms. 



The tapeworm is a flat worm which has lost 

 most of its organs on account of its parasitic 

 life. Its egg is picked up by an herbivorous 

 animal when grazing. The embryo under- 

 goes only partial development in the body 

 of the herbivorous animal, e.g. an ox. The 

 next stage will not develop until the beef is eaten by a 

 carnivorous animal, to whose food canal it attaches itself 

 and soon develops a long chain of segments called a 

 "tape." Each segment absorbs fluid food through its 



Fig. 79. — Sand 

 Worm x J 



(Nereis). 



Fig. 80. — Head 



of Sandworm 



(enlarged). 



