101 



NEMATODA— TRUE ROUND WORMS. 



Family TRICHINELLIDiE." 



Family DIAGNOSIS.— JVcmatorfo.- Elongate cylindrical worms; cephalic portion long 

 and very slender, caudal portion more or less swollen. Mouth rounded, without lips. 

 Esophagus relatively very long, composed of a single row of large cells, forming the 

 so-called "cell body" and supporting a narrow esophageal tube; anus terminal or 

 nearly so. 



Male: With a single spicule or without spicule. 



Female: With one ovary; vulva near caudal end of cell body, close to point where 

 body increases in diameter; oviparous or viviparous. 



Eggs: Oviparous species, with thick shell, with opening at each pole, closed by a 

 transparent plug. 



Type genus. — Trichinella Railliet, 1895. 



This family furnishes two parasites .to man: The whipworm {Tri- 

 churis trichiura) of the colon, and the trichina or flesh worm {Trichi- 

 nella spiralis, see p. 101). 



Genus TRICHINELLA b Railliet, 1895. 



Generic diagnosis. — TricMnellidx: Very minute worms, of nearly uniform diame- 

 ter. Adults in intestine of mammals, larvse encysted in muscles. 



Male: Without spicules, but with 2 conical appendages on the tail, at side of ter- 

 minal cloacal opening. 



Female: Vulva about one-fifth the length from anterior end; viviparous. 



Type species. — Trichinella spiralis (Owen, 1835) Railliet, 1895. 



TRICHINELLA SPIRALIS (Owen, 1835) Railliet, 1895. 



[Figs. 31 to 51.] 



Specific diagnosis. — Trichinella: Body thread-like, visible to naked eye. 



Male: Length, 1.4 to 1.6 millimeters; diameter, 40/(; distal of cloacal opening, 2 

 pairs of papillae, the anterior pair hemispherical, posterior pair conical. 



Female: Length, 3 to 4 millimeters; diameter, 60fx; anus terminal; vulva one-fifth 

 of length of body from the mouth; viviparous. 



Habitat. — Adults in lumen and wall of small intestine, encysted larvse in muscles 

 of various mammals, particularly in rats, mice, swine, and man. 



Geographic distribution. — ^More or less cosmopolitan. 



Source of infection. — From the life cycle of this parasite it is 

 clear that the permanent reservoir of infection must be some animal 

 with cannibalistic tendencies. Of the three most important hosts 

 (man, swine, and rats), the rats present ideal conditions in this 

 respect. It is true that there are some tribes of man which are 

 cannibalistic, but their distribution is restricted. Likewise swine 

 are in so far cannibalistic that they eat uncooked swine offal and 

 swill, but this is due to the shortsightedness of man rather than to 



o Synonym. — Trichotrachelidss. It becomes necessary under the international 

 code to change the family name; the family name TricMnellidx is chosen as less 

 likely to lead to confusion than a family name based upon Trichwis. 



b Synonyms. — Trichina Owen, 1835 [not Meig., 1830, insect.]; Trichinus Fraser, 

 1881a, for Trichina. 



