In the previous paper the author reported some interesting characters of the sexual organs in Sargassum filicinum. Notwithstanding the strong resemblance between S. horneri and S. filicinum in the external shape excepting the difference in the vesicular shape remarked by W. H. Harvey, they are distinguishable in sexuality : the former is strictly dioecious while the latter monoecious and androgynous in the receptacle. In April 1955, he happened to obtain another alga with the ellipsoidal or somewhat ovato-fusiform vesicles. It may not be identified with a typical form of S. filicinum and also not undoubtedly with S. horneri. In this paper the author intends to report the results of observations on this alga especially on the sexual organs and the embryo-development, and also to try some comparison with those of S. horneri and S. filicinum. The material were collected with some bottom gill-nets, chiefly at Hutae, Amakusa Islands, Higo Province. The results are summarized as follows : 1) The alga in question bears strong resemblance to both S. horneri and S. filicinum in having the disco-fibrous root, the fine spinous processes on stem, the cylindrical receptacles, and the alternato-pinnatisected leaves, but is different by having the ellipsoidal vesicles (Fig. 1). 2) The alga seems to mature about in April to May in Amakusa Islands, so is it in S. horneri, but comparing with the latter the former may be later slightly. 3) The receptacles are androgynous ; besides male and female conceptacles the same receptacle harbours hermaphrodite ones (Fig. 2), but the number of hermaphrodite conceptacles is indeed less than the others in each receptacle. The male conceptacles are not more than the female's, and they are found in any part of the receptacle, not being confined in the basal part as in S. filicinum ; though they gather more in the basal part. In the hermaphrodite conceptacle the oogonia and the antheridial hairs are not intermingled, but occupy the side position to each other. 4) Discharge of oogonia takes place periodically, and the discharged portion advances acropetally in each receptacle, as is usual in many other members of the genus Sargassum. 5) Discharged oosphere is ellipsoidal measuring ca 265 x 205 p, which is surrounded by a thick layer of mucilaginous substance. Around the outer wall of the thick layer there is observed a girdle-like dissolved portion as is reported on S. horneri (Kunieda & Suto 1940) and S. filicinum (Sawada 1955). 6) The embryo-development takes the same course with S. horneri. The rhizoid cell is segmented into 8 radially arranged cells (" radial 8-cell type " by Inoh 1930), and yet those 8 rhizoids developed from the rhizoid cell another group of about 7 to 15 rhizoids are observed to begin growth.