Abstract: This paper deals with the embryonic development of Lamprotula fibrosa.The fertilized eggs developed in the outer gill of the female. The cleavage wasunequal. When the natural water temperature ranged between 24-8℃, the embryonicdevelopment took 51 days. The fertilized eggs developed into mature glochidia afterthe cleavage and gastrula periods. The mature glochidia had transparent shells, hooks,thread of adductor muscle, inner byssus, setae and outer byssus. There were relationsbetween different stages of the embryonic development and the character of the outergill of the female.