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 color 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 earthworms ; including sandworms and leeches ; 2) 

 the roundworms, including trichina, hair- 

 worms, and vinegar eels ; 3) flativorms, 

 including tapeworm and liver fluke ; 4) 

 rotifers, which are mere specks in size. 



The tapeworm is a flatworm 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- 

 Fig. 80. — Head . 



of Sandworm goes only partial development in the body 



(enlarged). £ ^g 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 % 



(Nereis). 



