UNUSUAL ASPECTS OF INNER CELL MASS FORMATION, ENDODERM DIFFERENTIATION, REICHERT MEMBRANE-DEVELOPMENT, AND AMNIOGENESIS IN THE LESSER BULLDOG BAT, NOCTILIO-ALBIVENTRIS

Background and Methods: The early embryogenesis of the lesser bulldog bat, Noctilio albiventris (family Noctilionidae), was examined histolo gically in 59 pregnant females collected from a reproductively synchro nized population in Colombia. Results: Early blastocysts of Noctilio a re unusual in lacking a typical inner cell mass. Instead, cells inside of the trophoblast are dispersed for a period as a monolayer. A typic al inner cell mass (ICM) only forms and becomes properly oriented afte r the initiation of implantation. Several features of Reichert's membr ane in this species are also noteworthy: it develops between the ICM a nd trophoblast and between the parietal endoderm and trophoblast; it b ecomes linked to a meshwork of basal laminalike material that extends into the ICM; and it appears to be continuous, or fused, with prominen t basal laminae that develop within the cytotrophoblastic villi that r adiate throughout the preplacenta. Amniogenesis occurs by cavitation a nd converts the ICM into a hollow epiblastic vesicle. Gastrulation com mences before this vesicle exhibits obvious differentiation into an em bryonic shield and amniotic ectoderm. Conclusions: Because development and proper orientation of a typical ICM in Noctilio occur after the i nitiation of implantation, these may involve the migration of cells on the interior of the blastocyst and/or an unusual method of early endo derm differentiation. The possibility exists that epiblast, endoderm, and cytotrophoblast may all contribute to the secretion of Reichert's membrane in this bat. Although the early embryogenesis of Noctilio exh ibits many similarities to that in phyllostomid bats, substantial diff erences also exist between these closely related species. (C) 1996 Wil ey-Liss, Inc.