286 



GENERAL BIOLOGY 



of a loss of energy and vigor and a " shiftless- 

 ness " for which the " poor white " of the South is 

 famous. The group to which this worm belongs is 

 known as the Nematoda. They are all round, 

 often thread-like, with a thick cuticle, and they in- 

 fest many kinds of animals besides man. Another 

 intestinal parasite of a different sort is the tapeworm, 

 a representative of the " flatworms " or Platodes. 



FIG. 102. Parasitic worm in the body-cavity of a stickleback ; B, the 

 worm extended, enlarged l| times. (Gamble.) 



This is a ribbon-like worm of which the body is 

 broken up into a great many segments, all of them, 

 except the head segment, practically similar. This 

 worm, like the hookworm, attaches itself to the lining 

 of the alimentary canal of its (vertebrate) host and 

 is thus constantly bathed by the digested food 

 which the latter provides. Relieved of the necessity 

 of getting its own food, it has no need for sense 

 organs or for apparatus for eating, digesting, or 

 storing food. Digestive system and sense organs 



