A study on the ultrastructures of the prostate gland of Clonorchis sinensis was conducted. The presence of the prostate gland in this fluke has not been known up to present time. Authors observed the ejaculatory duct epithelium including its surrounding parenchyma and found the prostate gland with the help of the electron microscope. The prostate gland was consisted of numerous unicellular glands grouped around the ejaculatory duct. The individual cell was lobulated, tapering in the direction of the ejaculatory duct. The secreting ducts of the gland penetrated into the ejaculatory duct through the muscular layer and the basement membrane, and finally opened to the lumen of the ejaculatory duct. The secreting duct had single layered microtubules along the inner wall of the duct. The secretory bodies produced by the prostate gland seemed to be moved to the lumen of the ejaculatory duct through the secreting duct. The prostate gland of this fluke was less developed than that of Fasciola hepatica but the basic structures were quite similar. There were well-developed lamellae in the epithelia of all ducts concerning passage of spermatozoa from the testes to the male genital opening.
