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Trichotrachelidae — Body very long, anterior end produced into 

 a long and slender portion; posterior more or less swollen, containing 

 the genital organs. Mouth round and devoid of papillae; oesophagus 

 very long and traverses a peculiar strand of cells; no oesophagus 

 bulb. Anus terminal. Males with single or no spicule. Only one 

 ovary; vulva at the origin of the swollen part of body. Represen- 

 tative genera Trichuris and Trichinella. 



Eustrongylidae — Caudal bursa without thickened rays and with 

 a single spicule. Eustrongylus, Hystrichis. 



Spiruridae — Caudal bursa closed and vesiculate, entirely embrac- 

 ing the posterior extremity of the body. The two spicules unequal. 

 Physaloptera. 



Filaridae — Body long and filiform; mouth, of variable form, with 

 papillae, or with two lips. Oesophagus slender; no oesophageal bulb. 

 Males with coiled tail and with a single spicule or two unequal spicules. 

 Females with two ovaries; vulva at the anterior part of the body. 

 Representative genera Filaria, Spiroptera, Dispharagus. 



Gnathostomidae — Body cylindrical, covered for all its length or 

 merely anteriorly by chitinous lamellae, most of which have the 

 posterior border spinulate. Anterior extremity often swollen into 

 a globular head clothed with simple spines. Mouth with two lips, 

 a dorsal and ventral. Males with a spirally-coiled tail, whose 

 ventral face is provided with papallae, and with two spicules. Ovary 

 double, vulva back of middle of body. Oviparous. 



Anguilluidae — Small size, filiform ; mouth followed by a small . 

 cavity, the vestibule, containing a chitinous spine, or teeth. Oesopha- 

 gus swollen into a fusiform bulb, often followed by a second bulb, 

 with or without a dental armiture ; posterior third of the oesophagus 

 may be simply thickened. Males with two equal spicules; at times 

 with a caudal cuticular expansion. Ovary double; vulva posterior 

 of middle. Oviparious. Most of this group are free-living. Anguil- 

 lula. 



Angiostomidae — Heterogenos forms, that is, having two types 

 of sexual generations. Genus Strongyloides. 



