In this paper are reported the egg development and hatched larvae of Monacanthus cirrhifer Temminck et Schlegel by artificial insemination carried out on July 12, 1954, at Oshima near Fukuoka City. The spawning season seems to extend from early June to middle of July in the vicinity of Fukuoka City, Kyushu. The egg is demersal and strongly adhesive, colorless, and spherical in shape, measurlng 0.61-0.66 mm. in diameter, with 4-5 large colorless oil-globules measuring 0.05-0.14mm. accompanied by numerous smaller ones. Two hours after insemination, the first division was finished; in 5 hours and 30 minutes it attained the morula stage; in 23 hours the blastopore was closed; in 42 hours and 30 minutes, xanthophores appeared on the embryonal body, with 15 myotomes; in 50 hours, melanophores appeared on the head of the embryo. Hatching took place in about 58 hours at the water temperature 18°-21℃. The newly hatched larvae measured 1.80-2.07 mm. in total length, with myotome number 6+14=20. The yolk was oval, measuring 0.50-0.55 mm. in long axis, with only one oil-globule measuring 0.12-0.17mm.at its anterior end. The pectoral fins were already formed. Melanophores were found on the head and the yolk surface and also along the ventral side of abdomen. Ⅹanthophores formed 3 cross bands in the caudal part. The larva 90 hours old measured 2.50mm. in total length, and wholly absorbed the yolk. The cross bands of xanthophores disappeared, and the melanophores were seen along the whole ventral margin of the tail.
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