Cynoglossus robustus Gunther is a common sole, distributed from the middle Japan to the southern China Sea. It inhabits mud or sandy mud bottom. The spawning season seems to extend from the end of June to early August in northern Kyushu. On July 20, 1956, at Moji City, Kyushu, the authors carried out the artificial insemination of this fish, and observed the egg development and hatched larvae (Plate 17 : Figs. 1~8). The egg is bouyant and colorless, spherical in shape measuring 0.85~0.90mm in diameter, with 5~15 colorless oil-globules measuring 0.050~0.075 mm. The outer surface of egg-membrane has faint, fine, hexagonal network sculpture. Hatching took place in 16.5~17.5 hours at the water temperature 17.5~26.2℃. Newly hatched larva (Plate 17 : Fig. 4) is 1.75~4.85 mm in total length with 40~45 (13+27~32) myotome (The number of vertebrae of this fish being 9+48~49=57~58). The yolk is oval, 0.8 mm in long axis, with 5~15 oilglobules. Small melanophores and xanthophores are distributed on the head, trunk, tail and yolk-surface. The larval fins are free from any chromatophores. In six hours after hatching, the larva attains 2.2~2.5 mm in total length (Plate 17 : Fig. 5) with 57~58 (12~13+45) myotome. Xanthophores form three cross bands in caudal part of the larva. In one day after hatching, the anus of the larva which was situated under 12~13th myotome advances forward to under 9th myotome (Plate 17 : Fig. 6). In three days larva attains 3.6 mm in total length and the yolk is entirely consumed (Plate 17 : Fig. 8). Above the head, at the anterior end of the dorsal membranous fin, a small spinous process is formed.
イヌノシタ Cynoglossus robustus Gunther はウシノシタ亜目Soleinaのウシノシタ科Cynoglossidaeに属し本州中部以南から南支那海に分布し, 泥質か砂泥質の海底に棲息する. ウシノシタ類の卵および仔魚についてはEhrenbaum, E(1905,1909), 神谷尚志(1922), Nair, R. V. (1902), Seshappa, G. et al. (1955)の諸氏の研究がある. 筆者等は1956年(昭和31年)7月, 門司市柄杓田(瀬戸内海側)の底刺網漁船に乗つてイヌノシタの人工授精を行い, 孵化後約5日間飼育観察したので卵発生および仔魚前期について報告する.