Some early blastocysts of Bettongia cuniculus are described, ranging from the young unilaminar stage to that showing the first appearance of the mesoderm. The formation of formative and non-formative areas is described, and the origin of endoderm and mesoderm. Endoderm arises as a number of endoderm mother cells distributed throughout the formative area which move out of their positions in the blastocyst wall on to the inner surface of the formative ectoderm; later they join up to form a continuous layer. The process, therefore, is very similar to that found in Dasyurus viverr i n u s by Hill; the formation of endoderm from large included cells as found by Hartman in Didelphys virginiana does not occur here. Mesoderm arises as an oval area of active proliferation in the formative ectoderm, orientated from near one edge of the still circular formative area towards the centre.
- Copyright © 1934 by the Company of Biologists Ltd.