Studies on the embryology of microchiroptera Part V. Placentation in the vespertilionid bat- Scotophilus wroughtoni (Thomas)

Abstract

1. The yolk-sac which is disposed towards the mesometrial side establishes placental relationship with the uterus. The yolk-sac placenta is at first non-vascular and later becomes vascular. 2. As development proceeds the extension of the exocoelom and the expansion of the amniotic cavity results not only in the obliteration of the yolk-sac placenta, but, in the invagination of the yolk-sac roof over the distal bilaminar omphalopleure. 3. The allantois is disposed towards the antimesometrial side. The allantois gradually spreads towards the lateral sides below the placenta and progressively replaces the yolk-sac placenta. 4. The changes involved in the formation of the definitive labyrinthine placenta are : (i) The penetration of the syncytiotrophoblast by the tropho-blastic chords, (ii) the invasion of the cavities thus formed by the allantoic mesenchyme and foetal vessels, (iii) the loss of the cell boundaries in the cytotrophoblastic cords, which therefore occurs as a network of cytoplasm with flattened nuclei embedded in rows. 5. The final placenta is therefore of the labyrinthine hasmochorial type.