CHAPTER XVIII. 



THE ROUND WORMS. 



CLASSIFICATION OF THE NEMATHELMINTHES (ROUND WORMS). 



Class. 



/O 



Nematoda, 



Acanthocephala, 

 Hirudinea, 



NOTE. The Strongyloides stercoralis was formerly described under two desig- 

 nations: (i) Anguillula intestinalis, a parasitic generation and (2) Anguillula ster- 

 coralis, a free living generation. 



ROUND WORMS OR NEMATODES. 



All nematodes are covered by a cuticle which varies in thickness. 

 The sexes are, as a rule, separate. The male can usually be recognized 

 by its small size, its curved or curled posterior end, and at times exhib- 

 iting an umbrella -like expansion the copula tory bursa. The spicules, 

 chitinous copulatory structures, may be observed drawn up in the 

 worm or projected out of the cloaca. 



Certain papillae in the region of the anus are valuable in differen- 

 tiation. In the female the vulva is usually situated about the middle 

 of the ventral surface. 



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