226 PARASITES OF THE DOMESTIC ANIMALS 



absent; preanal sucker neaiij^ circular and limited by a chitinous ring; 

 spicules equal or unequal. 



Subfamily Heterakinse, Railliet and Henry, 1912. 



Type-genus Heterakis, Dujardin, 1845. 



"Mouth with simple, usually inconspicuous Hps. Male usually with 



one spicule, at times reduced, imperfectly chitinized or absent. Caudal 



extremity of female much elongated and sublobate. Vulva anterior. 



Eggs characteristically flattened on one side. 



Family Ox;ynaridse, Cobbold, 1864. 



Subfamily Oxjiirinse, Hall, 1916. 



Type-genus Ox^auis, Rudolphi, 1803. 



''Males with a well-developed caudal bursa supported by rays; in 



forms near the outer limit of the superfamily the bursa is occasionally 



verj^ small and the rays atj^pical, or the bursa may be lacking altogether. 



Esophagus without posterior bulb. Mouth naked or with a buccal 



capsule and six papillae, distinct or indistinct. Male usually with two 



spicules and female usually with two ovaries. Oviparous or viviparous. 



Superfamily Strongyloidea, Weinlancl, 1858. 



"Buccal capsule present. Bursa highly developed, with a typical 



system of supporting rays consisting of one or two dorsal raj'S and two 



lateral ray systems of six rays each. Male with two spicules and female 



with two ovaries. Vulva at times anterior to the middle of the body, 



but usually posterior of the middle. Oviparous, eggs segmenting when 



laid. Development, so far as known, direct. Embryo rhabditiform. 



In digestive, rarely in respiratory system. 



Type-family Strongylidae, Cobbold, 1864. 



"Buccal capsule present. In digestive, occasionally in respiratory, 



system. Development direct, at tunes complex, involving cutaneous 



infection, nodular development or other embryonic or larval migration. 



Subfamily Strongylinae, Railliet, 1893. 

 Type-genus Strongylus, Mueller, 1780. 

 "Simple mouth without a buccal capsule. Parasitic only in the di- 

 gestive system. Development direct and simple, involving in all cases 

 known only the possibility of infection by ingestion. 



Family TrichostrongyUda), Railliet, 1915. 

 ' ' Body straight or curved, but not regularly coiled in a spiral . Females 

 with two ovaries. 



Subfamily Trichostrongylinse, Leiper, 1908. 

 Type-genus Trichostrongylus, Looss, 1905. 

 "Buccal capsule present or absent. Bursa present or absent; when 

 present, frequently atypical in structure and number of rays. Ovip- 

 arous, with eggs in variable stages of segmentation when oviposited, 

 or viviparous. Embrj'o not rhabditiform. Usually in respiratory and 

 circulator}' S3^stems, rarely in digestive sj-stem. 



