Geographical distribution.—It has been reported from Egypt, China, and Japan, and probably has a wide distribution.
Zoological distribution.—Looss has found it in Egypt in the dog (Canis familiaris), in the cat (Felis domestica), in a fox (Canis niloticus?), and in a kite (Milvus parasiticus). Janson reports it from the intestine of the dog in Japan, and Yokagawa in Formosa.
Fig. 195.—Heterophyes heterophyes.
a, Greatly magnified; b, natural size.
The parasite.—H. heterophyes (Fig. 195) is the smallest trematode inhabiting man, excepting Yokagawa yokagawa. It measures 1 to 1.7 mm. in length by 0·3 to 0·7 mm. in breadth. It has an oval, elongate shape and a reddish colour. The neck is not sharply defined from the body, and may be greatly outstretched. The oral sucker (0·09 mm. in diameter) is subterminal and about one-third the size of the ventral sucker (0·23 mm.), which is placed at about the middle of the body. The cuticle is thickly beset with quadrate scales, 5 to 6 μ long by 4 μ broad. The prepharynx is short (80 μ in length); the pharynx measures 50 to 70 μ, in length by 40 to 50 μ in diameter. The œsophagus is about three times as long. The intestinal cæca extend to the posterior extremity, where they converge and terminate close to the excretory bladder. The lateral ends of the vitellaria extend beyond the intestinal cæca. The genital pore opens postero-laterally to, and in the immediate vicinity of, the ventral sucker; it is surrounded by a muscular ring. Testicles oval, in extreme posterior end of body. Ovary globular, median and anterior to the testes. Receptaculum seminis as large as the ovary; uterine coils not numerous, and extending between the ventral suckers and the testicles. Eggs light brown, thick-shelled, oval, 20 to 30 μ by 15 to 17 μ; contain a ciliated embryo when oviposited. (Fig. 169, c.) The life-history of the parasite is not determined. It seems to have little pathological importance. It inhabits the small intestine.
Yokagawa yokagawa (Katsurada, 1912)
Synonyms.—Tocotrema yokagawa, Heterophyes yokagawa; Metagonimus yokagawai (Katsurada).
