抄録
本論文は, 異なった成長期の24例の南半球産ミンククジラ Balaenoptera acutorostrata の胎仔における歯芽発生とその生理的退行およびヒゲ板の発生を肉眼解剖学的および組織学的に観察したものである. その結果, この種の歯芽の初期発生パターンが陸生哺乳類の乳歯の発生および生理的退行と類似している事が示された. 退行中の歯芽は胎長615mm以上の個体で確認され, 退行現象は歯芽の表面全域で進行しているようであった. このことは, 陸生哺乳類の乳歯の退行が歯根部に限局されている点と異なっていた. 次いで歯芽の発生数は, 胎長135-153 mmの胎仔において下顎より上顎で数多く確認された. また, 本研究では歯芽の発生数はばらついていた. 退行中の歯芽と共にピケ板の原基が船長903mmの個体で検出され, 歯芽の退行がヒゲ板の原基の発生を誘導していることが示唆された.
The development and degradation of temporary tooth buds and the development of rudiment of baleen plate were observed by gross-anatomical and histological examinations in twenty-four fetuses of the southern minke whale, Balaenoptera acutorostrata. The primary patterns of development of tooth buds were similar to those of deciduous tooth buds in the terrestrial species. Degradation of tooth buds was observed in the fetuses more than 615 mm body length (BL) and might proceed throughout the dental surface of the tooth buds. That degradation pattern was a little different from that of deciduous tooth buds in terrestrial species, which has a limited degradation area at the root of the tooth buds. In the fetuses with 135 and 153 mm BL, the upper jaw had a larger number of tooth buds than the lower jaw, although the number of buds varied in different individuals. Formation of rudiment of baleen plate was observed with degraded tooth buds in the fetus of 903 mm BL and it may be induced by the degradation of tooth buds.
