Development of the External Genitalia in Fetuses of the Southern Minke Whale, Balaenoptera acutorostrata

• Published in: Cells Tissues Organs
• Main Authors: Amasaki, Hajime, Ishikawa, Haime, Daigo, Masayuki
• Format: Article in Journal/Newspaper
• Language: English
• Published: S. Karger AG 1989
• Subjects: Balaenoptera acutorostrata; minke whale
• Online Access: http://dx.doi.org/10.1159/000146744; https://www.karger.com/Article/Pdf/146744

The developmental changes of the anogenital distance and external genitalia were studied in 81 fetuses of the southern minke whale. It was difficult to sex the fetuses with less than 55.8 mm crown-rump length (CRL) even by histological means, but it was easy in the fetuses with more than 77.0 mm CRL and less than 110.0 mm CRL. The histologically determined male fetuses had a ratio of anogenital distance to CRL or body length of more than 5% while females had a value of less than 4%. At later stages with a CRL of more than 113.0 mm, male fetuses had an umbilicus-directed genital tubercle, while in females a tail-directed tubercle was observed.The present study suggests that the stage with sexual dimorphism might be earlier in the southern minke whale than that previously reported.