PREGNANCY IN CHIROPTERA

As with other aspects of their biology, bats exhibit considerable dive rsity in their reproductive characteristics. While early embryonic dev elopment in many species generally adheres to the pattern shown by mor e commonly studied eutherian mammals, others demonstrate advanced deve lopment in the oviduct (to the zona-free blastocyst stage) and a prolo nged tubal journey of the embryo in a temporal sense. In some bats, th e process for transporting ova through the oviducts can distinguish be tween living embryos and the remnants of dead ova. Implantation in bat s is unusually diverse with respect to localization of the nidation si tes (which in most species seem to be predetermined), orientation of t he inner cell mass during implantation, depth of implantation, and tro phoblastic invasiveness. Some species which can be bred in captivity w ould appear to be promising experimental models for studies of implant ation because both this process and their endometrial biology in gener al exhibit many similarities to those of humans. Depending upon the sp ecies, bats develop either endotheliochorial or hemochorial placentas. Studies on black mastiff bats (Molossus ater) indicate that maternal endometrial endothelial cells probably play a very important morphogen etic role during placental development in this species. Similarities i n placental structure suggest that this may also be the case in a numb er of other eutherian mammals. (C) 1993 Wiley-Liss, Inc.