NEMATHELMINTHES. 15s 
Ascaris is a fair type of the numerous NEmatTopa 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 Vematoda, 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 Zyichina being known as ¢vichinosed pork. 
Introduced into the human subject, they give rise to ¢richin- 
osis. The Fi/aride also produce dangerous diseases, and the 
eel-worms or Anguillulide cause great destruction to crops. 
Fig. 88.—MAGNIFIED VIEW OF ‘‘ TRICHINOSED” PoRK. THE 
NEMATODE WoRMS (TRICHINA SPIRALIS) ARE SEEN 
ENVELOPED, IN THEIR CAPSULES. 
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