The body is of a faint reddish-brown colour and plump oval shape. The ventral surface a little flattened; 7·5 to 12 mm. in length, 4 to 6 mm. in breadth, and 3·5 to 5 mm. thick (in man). The oral sucker (0·75 mm.) is subterminal; the ventral sucker (0·8 mm.) somewhat in front of the middle of the body. Pharynx spherical, 0·3 mm. in diameter, or 0·4 by 0·3 mm.; œsophagus, 0·02 mm.; intestinal cæca convoluted, asymmetrical, the first part having the same structure as the œsophagus. The cuticle is covered with spines in groups; the excretory pore opens at the posterior end rather on the ventral surface, the excretory ducts open into the elongated bladder at the hind end near the pore. Genital pore behind the ventral sucker and median. Genital sinus 0·2 mm. long with thick wall, ejaculatory duct 0·13 mm., pars prostatica 0·2 mm., seminal vesicle duct-like of irregular outline. Behind the sucker the ovary on the left, and the closely packed uterine coil on the right (though amphitypy of these two organs is common); the two irregularly lobed testes lie side by side posteriorly. Vitellaria extensive, leaving only a median dorsal and ventral space free. Seminal receptacle probably absent; Laurer’s canal present. The eggs are oval, brownish-yellow, fairly thin shelled, and measure on an average 81·2 µ by 49·2 µ. [Illustration: FIG. 149.--_Paragonimus ringeri_, Cobb.: to the right, dorsal aspect; to the left, ventral aspect. Natural size. (After Katsurada.)] [Illustration: FIG. 150.--_Paragonimus ringeri_, Cobb.: diagram of the internal organs. _a_, œsophagus; _b_, vitellaria (a portion only shown); _c_, common genital duct; _d_, shell gland with oviduct, Laurer’s canal and vitelline duct; _e_, ovary; _f_, vitelline receptacle; _g_, excretory pore; _h_, oral sucker; _i_, pharynx; _k_, gut; _l_, ventral sucker; _m_, uterine coils; _n_, vitellarian ducts; _o_, vas efferens; _p_, testis. (After Kubo.)] [Illustration: FIG. 150A.--_Paragonimus westermanii_, Kerb.: seen from the ventral surface. Mouth, pharynx, intestinal cæca, at the sides of which the vitellaria are observed. The genital pore is behind the ventral sucker, and next to it, on the left, the ovary; on the right, the uterus; the two testes posteriorly; the excretory vessel in the middle, 10/1. (After Leuckart.)] The following species are also known:--_P. westermanii_, Kerb., 1878, in the tiger, and _P. kellicotti_, Ward, 1908, in the pig, dog, and cat (N. America). Ward and Hirsch give the following differences between the spines of the three forms:-- _P. ringeri._ _P. westermanii._ _P. kellicotti._ Shape Chisel-shaped, Lancet-shaped, Chisel-shaped, moderately heavy. very slender. heavy. Distribution Circular rows, in Circular rows, Circular rows, groups. in groups. singly.