In order to observe the infectivity, growth and development and adult morphology of Metorchis orientalis, a total of 40 chicks were experimentally infected with 100 metacercariae respectively, collected from Pseudorasbora parva. The worms of various developmental stages were recovered from chicks at 1.5, 3, 5, 7, 9, 11, 14 and 21 days after infection, and they were prepared for morphological observations and measurements. All of the worms were found in the gallbladders of chicks, and their recovery rate was 32% in average. The growth of the body was rapid from 9 to 11 days after infection. The genital primordia appeared in 1.5 and 3-day old worms, and ovary and testes were first observed in 5-day old worms. Thereafter, genital organs gradually matured and completed up to 11 days after infection. The adult worm was leaf-like, and possessed a convoluted tubular seminal vesicle, an ovoid ovary, a sac-like seminal receptacle, 2 lobed-testes and follicular vitellaria. Eggs were 31.9 x 15.3 microns in average size, ellipsoid to elliptical in shape and possessed abopercular thickenings. From the above results, it is concluded that M. orientalis grows in sigmoid pattern in chicks, and their genital organs fully mature between days 9 and 11. It is also confirmed that a chick is a new definitive host of M. orientalis.
