SEM studies on amphibian gastrulation have shown the overall shape and arrangement of several cell types (e. g. bottle cells, mesodermal cells, ectodermal cells, etc. ) as well as the cellular activities in the blastocoel cavity during archenteron floor descent. The main purpose of the present communication is to show the internal structure of Bufo arenarum gastrula as viewed in sagittal dissection at the stage when the ventral blastoporal groove starts forming.Material and Methods: Bufo arenarum gastrula were fixed in 2, 5% glutaraldehyde in phosphate buffer for 2, 5 hrs. After removing the vitelline membrane the embryos were fractured and then dissected near the mid-sagittal plane. The specimens were dehydrated through an acetone series, dried according to the critical point technique, coated with evaporated gold-platinum and observed in a Jeol JSM-U3 scanning electron microscope operated at 5-15 kW.Observations: The internal structure of a Bufo arenarum gastrula at the ventral blastoporal groove stage is illustrated in Fig. 1. Blastocoel cavity (B), internal endodermal yolky cells (Y), prospective ectoderm (PE), archenteron (A), dorsal blastoporal lip (L), ventral blastoporal groove (V).