NEMA THELMINTHES. 



155 



Ascaris is a fair type of the numerous Nematoda or 

 threadworms which infest the body of the higher animals. 

 Its characters belonging to the class are the unsegmented 

 body, the absence of appendages and the characters of the 

 body-wall, excretory and reproductive systems. 



PHYLUM NEMATHELMINTHES. 



This phylum contains a great number of free and parasitic 

 worms forming the class Nematoda^ and another divergent 

 class of parasitic worm called Acanthocephala. The latter 

 have a hooked anterior process and no alimentary canal, 

 showing a complete adaptation to enteric parasitism, but the 

 former show few similar modifications. Some appear to be 

 only occasionally parasitic and some are entirely free. 

 Trichina spiralis infests the pig, the muscles of this animal 

 with encapsuled Trichina being known as trichinosed pork. 

 Introduced into the human subject, they give rise to trichin- 

 osis. The Filaridce also produce dangerous diseases, and the 

 eel-worms or Anguillulidce. cause great destruction to crops. 



Fig. '^%. — Magnified View of "Trichinosed" Pork. The 



Nematode Worms (Trichina Spiralis) are seen 



Enveloped in their Capsules. 



