The intermediate host is still unknown. Leuckart for some time held the opinion that small species of Planorbis from fresh water, which contain encysted Distomata, were to blame, and he supported his views by a feeding experiment which seemingly yielded positive results; this, however, is not definitely proved. Piana’s statement that small land snails are the intermediate hosts has also not been proved.
Fig. 168.—Echinostoma ilocanum. Vo., oral sucker; Ph., pharynx; Cirre, cirrus; V.v., ventral sucker; Ut., uterus; G.c., ovary; Ov., shell gland; T., testes; T.d., vitellarium; C.ex., excretory vesicle. (After Brumpt.)
Family. Echinostomidæ, Looss, 1902.
Sub-family. Echinostominæ, Looss, 1899.
Genus. Echinostoma, Rud. 1809; Dietz, 1910.
Fore-body not bulging. Greatest width at or behind the ventral sucker. Oral sucker not atrophied. Collar kidney-shaped with a double dorsally unbroken row of spines, terminating in four to five angle spines. The border spines of the aboral series not larger than the oral. Skin spined or smooth. Body elongated. Uterus long with numerous transverse coils. Ventral sucker in the anterior quarter of body. Cirrus sac small, almost completely in front of the ventral sucker. Testes round or oval, smooth incurved or lobed, in the hinder half of body. Ovary median or lateral in front of testes. Vitellaria from hinder margin of ventral sucker to end of body. Eggs oval, 84 µ to 126 µ by 48 µ to 82 µ.
The spines placed most ventrally, or those placed most medially on ventral surface, are from differences of position or form termed “angle” spines, the rest “border” spines.
Type.—Echinostoma echinatum, Rud.