Metacercariae parasitic on the loach living in Ashida River, Hiroshima Prefecture were examined by applying the artificial gastric juice digestion method to twenty loach which weighed from 28g to 46g, As a result, Metagonimus yokogawai was the largest in number, that is, its average number per loach was 18.8 on scales, 3.1 on gills, and 2.8 on muscles. Next to the largest was Centrocestus nycticoracis i.e., 5.1 on gills. Echinostoma cinetorchis, 1.6 on gills. Echinostoma hortense, 2.5 on the inter-ventral membrane. Echinochasmus perfoliatus, 0.9 on gills.
Metacercariae of Metagonimus yokogawai thus collected were given to nine birds and also to five rats for the sake of contrast through mouth in such a way as follows; 50 metacercariae to every five chickens, from 250g to 325g in weight, the same to every two canaries 82g and 88g in weight, the same to every two white-eyes, 46g and 48g in weight and the same to every five rats, from 98g to 120g. Afterwards, observation and studies were made on the number of metacercariae parasitic site, number of eggs in the uterus, first day of ovulation, size of eggs, and developing speed of the body in different hosts.
As a result, of 50 metacercariae given to each host, average 6.4 were detected in the chicken, 6 in the canary, 1.5 in the white-eye, and 17 in the rat. In both the cases of birds and rats, the parasitic site was mainly below the middle part of the small intestine. Difference in the developing speed of the body in different hosts was not perceived. Ovulation began on the ninth day in rat, on the 10th day in chicken, on 18th, in canary, and in the case of the white-eye, ovulation had not yet begun on the 10th day when it was dissected. Average size of eggs taken from 200eggs was 0.0324×0.0208mm.
Hereby the author has decided to name this species as Metagonimus yokogawai takahashii.