Implantation, development of the fetal membranes, and placentation in the captive black mastiff bat, Molossus ater

Abstract

Uterine events during pregnancy were examined histologically in laboratory-bred black mastiff bats (Molossus ater) as part of an effort to develop this species as a model for studies of the factors controlling trophoblastic growth. Embryos entered the uterus at the morula stage and in most cases shed their zonae pellucidae reasonably intact, apparently as blastocyst expansion occurred. Implantation was superficial and observed to occur only in the right uterine horn. During implantation to the endometrium by both blastocyst expansion and closure of the uterine lumen. A decidual reaction was evident at an early stage of uterine epithelial displacement and spread rapidly through the endometrium. Initial trophoblastic proliferation occurred along the uterine lumen and into the glands, while its invasion of the endometrial stroma was delayed. Although one or several primordial cavities have been observed to develop within the epiblast during implantation, these subsequently opened to a trophoepiblastic cavity, and the definitive amnion was formed by folding. A choriovitelline placenta was present briefly at thesomite stage, but disappeared as the exocoelom enlarged and the yolk sac collapsed. The latter persisted through pregnancy, however, as a glandular-appearing body. As the yolk sac retracted from the chorion, it was replaced by allantoic mesoderm, creating a diffuse labyrinthine endotheliodichorial placenta. This was prominent during mid-gestation, but was supplanted by the discoidal hemochorial placenta as the major site of feto-maternal exchange during late pregnancy.

Embryonic Staging System for the Black Mastiff Bat,Molossus rufus(Molossidae), Correlated With Structure‐Function Relationships in the Adult

“…It has been well-documented elsewhere that M. rufus does not exhibit a limited period of estrus (Rasweiler, 1987(Rasweiler, , 1988(Rasweiler, , 1990b. Instead, most females usually exhibit intermittent brief periods of sperm-positive vaginal aspirates, as well as one or more longer periods of such aspirates.…”

“…Most females exhibited an extended period of sperm-positive aspirates, however, and the time elapsed from its onset was generally correlated with the stage of embryonic development found in pregnant animals. Records of the days on which sperm-positive aspirates were obtained from many of the bats have been published elsewhere (Rasweiler, 1988(Rasweiler, , 1990b.…”

“…On dissection, the greatest diameter of the right uterine horn was measured. In the initial studies (Rasweiler, 1990b), embryos at the limb bud stage or later were removed from the uterus, weighed, fixed in Zenker's fluid for 16-20 hr, and measured. The embryos were then washed overnight in running tap water and dehydrated through graded alcohols to 70% ethanol for storage.…”

“…Both embryonic weight and crown-rump length of each embryo were then recorded postfixation. These measurements have been recorded in Rasweiler (1990b) and Table 1 of this article.…”

“…a Measurements reported in Rasweiler, 1990b. b Measurements not included in Rasweiler, 1990b; C-R length and weight recorded postfixation. Counted from the beginning of a prolonged period of sperm-positive vaginal aspirates.…”