SEA CUCUMBERS. 233 



PARASITIC WORMS. 



There are a great number of Worms which hve as 

 parasites in the intestines, or in the flesh of other ani- 

 mals. Such are the Tapeworms and the Threadworms. 

 The Trichina is the most dangerous of these parasites. 

 It Hves in the flesh of the hog, and if eaten by man 

 the worms develop in the intestine and afterwards 

 burrow out into the muscles. Their migration causes 

 great suffering and often death. 



The Gordius, or Hair Worm, belongs to the same 

 great group of Worms as the Trichina. It lives, when 

 young, in the intestine of the Cricket and Grasshopper 

 but becomes free when grown up. It lays its eggs in 

 the water, where it is often found and sometimes 

 thougrht to be an animated hair. 



ECHINODERMS, OR STARFISHES. 



The word Echinoderm means Iiedgeliog-skin, and is 

 given to these animals because many of them have the 

 outside covered with spines, thus reminding us of the 

 Hedgehog of the fields, described on page 60. In the 

 Echinoderms the parts are arranged according to a 

 reigning number, generally five ; that is, the parts of 

 each kind are five, or a multiple of five. 



SEA CUCUMBERS, OR HOLOTHURIANS. 



The Holothurians, or Sea Cucumbers, have no spines, 

 but are covered with a tough skin capable of great ex- 

 pansion and contraction, and containing particles of 

 limestone. There are many kinds, varying from an 



