CHAPTER XVIII. 



THE ROUND WORMS. 



CLASSIFICATION or THE NEMATHELMINTHES (ROUND WORMS ) . 



Class. 



Nematoda 



Family. 

 Angiostomidae 



Filariidae 



Genus. 



Species. 



Trichotrachelidae 



Strongylidae 



Ascaridae 



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, 

 and is frequently ringed. The cuticle is moulted three or four times. 

 The cuticle is formed by the underlying ectoderm which is, as a rule, 



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