38 THE ROUND WORMS OF DOMESTIC SWINE. 



KEY TO THE ROUNDWORMS PARASITIC IN DOMESTIC SWINE. 



The arrangement of the following key to the roundworms which 

 have been reported by various authors as parasites of hogs is purely 

 artificial and arbitrary and indicates nothing as to the systematic 

 relationship of the different forms. A classified list of the round- 

 worms of swine is given later on page 41. 



Section. 



Parasitic in alimentary tract 1 



Parasitic in respiratory tract 16 



Parasitic in other organs 17 



1. Diameter of body at middle over 3 mm 2 



Diameter of body at middle less than 3 mm 3 



2. Anterior extremity furnished with a protractile prolwscis covered with spines. 



Male 6 to 10 cm. long, 3 to 5 mm. in diameter. Female 20 to 35 cm. long, 

 4 to 9 mm. in diameter. Eggs, 87 to 100 n long, subcylindrical, smooth, 

 with 3 envelopes. In small intestine, usually attached to the mucous 



membrane Gigantorhynchus hirudinareus. 



Anterior extremity without protractile proboscis. Mouth with 3 prominent 

 lips. Male 15 to 17 cm. long, 3 to 3.2 mm. thick. Female 20 to 25 cm. 

 long, 5 to 5.5 mm. thick. Eggs oval, 66 fi long, thick-shelled, surface cov- 

 ered with mammillate projections. In small intestine, sometimes in biliary 

 tract and pancreas Ascaris suum. 



3. Less than 5 mm. in length 4 



Over 5 mm. in length 5 



4. Vulva anterior of middle of body. Ovoviviparous. Females 3 to 4 mm. 



long, 60 fi in diameter. Males 1.4 to 1.6 mm. long, 40 /z in diameter, with 

 a short finger-like process on each side of the anal opening. Adults in 



small intestine, larvae encysted in skeletal muscles Trichinella spiralis. 



Vulva posterior of middle of body. Females (parthenogenetic; parasitic 

 males lacking) 3.75 mm. long, 80 fi in diameter. Eggs 45 fi long by 25 /t 

 broad, with thin shells. In small intestine Slrongyloides suis. 1 



5. Head covered with spines; separated from the body by a deep constriction. 



Male 15 to 25 mm. long. Female 22 to 31 mm. long. Eggs 70 fi long by 39 



fi wide. In stomach Gnathostoma hispidum. 



Head without spiny armature 6 



6. Posterior end of body of female with relatively large rosette-like excrescence 



containing the hypertrophied uterus. Male 12 mm. long. Female 15 mm. 



long. In stomach Simondsia paradoxa. 2 



Posterior end of body of female without uterine rosette 7 



7. Anterior portion of body slender, like a whiplash, about twice as long as the 



thicker posterior portion. Male with single spicule. Male 33 to 40 mm. 

 long. Female 34 to 50 mm. long. Eggs 52 to 56 /* long, ellipsoidal, with 

 an opening at each pole closed by a plug-like operculum, and brownish in 



color. In cecum Trichuris suis. 



Body continuous, not flagelliform anteriorly. Male with two spicules 8 



1 While Strongyloides papillosvs (= Trichosoma papiUosum Wedl.)a parasite of sheep has frequently been 

 reported for the pig, this is probably the result of confusion with Strongyloidu suis. The Stronyyloides of 

 the pig Is somewhat larger than the form found in sheep. 



* Included by the present writer among the Filariidse on account of the inequality of the spicules. Its 

 position in this family is not, however, defin tely established. See footnote on page 9, second paragraph. 



