74 TROPICAL MEDICINE AND HYGIENE 



free-living in water. The alimentary canal is usually 

 degenerate. 



(3) Acanthocephala have no mouth or alimentary 

 canal. They have a protrusible proboscis, covered with 

 numerous rows of hooks. They are common parasites in 

 birds, but have been found parasitic in man. They are 

 more likely to be mistaken at a superficial examination 

 for Cestoda than recognized as Nematoda. 



NEMATODA. 



Nematoda are a very large class including free-living 

 forms, forms living in decaying vegetable matter, and 

 forms parasitic not only in invertebrates and vertebrates 

 but in plants. The life-history varies greatly in the 

 different families. The Nematoda parasitic in man 

 belong to the families : 



(1) Anguillulidae, e.g., Rhabdis. 



(2) Angiostomidae, e.g., Strongyloides intestinalis. 



(3) Filariidae, e.g., Filaria bancrofti, F. loa, F. perstans, 

 F. medinensis, and F. -volvulus. 



(4) Trichotrachelidae, e.g., Trichocephahis trichiurus or 

 dispar, and Trichina spiralis. 



(5) Strongylidae, e.g., Ankylostoma duodenale, Necator 

 americanus, Triodontophonis diminutus, (Esophagostomum 

 apiostomum (vel brumpti). 



(6) Gnathostomida3, e.g., Gnathostoina siamense. 



(7) Ascaridce, e.g., Ascarls lumbricoides, A. mystax, and 

 A. caninum, and Oxynris vermicularis, Physaloptera 

 Hiordens. 



The separation into families is based on several differ- 

 ent characters. Amongst these the most important are 

 (i) the character of the mouth and oesophagus; (2) the 

 arrangement of the genitalia, and especially of the male 

 genitalia; (3) the life-history ; (4) the general characters. 



Anguillulidcc.A\\ small worms. The head is not pro- 

 vided with any armature and there is a double dilatation 

 of the oesophagus in the adult form. 



