Placental development in the mongolian gerbil ( Meriones unguiculatus ). I. Early development to the time of chorio-allantoic contact This investigation was supported in part by Institutional Research grants IN-40I and IN-40J to the University of Michigan by the American Cancer Society, by a General Research Support grant to the University of Michigan Medical School, and by Michigan Memorial Phoenix Project 428.

Abstract

Early gerbil development was studied from days 4 through 12 of gestation. Implantation occurs on day 8 in a shallow antimesometrial implantation crypt. The proamniotic cavity forms from an invagination of basal trophoblast and a folding together of the rim of the cup thus produced. The approximation of this rim gives rise to the ectoplacental cone. The further development and expansion of the ectoplacental cone is much like the rat. Amniogenesis is by folding into the proamniotic cavity. Between large glycogen-filled decidual cells occur many PAS-positive eosinophilic granular cells. A massive subplacental gland forms from proliferating uterine epithelium within the decidua basalis. Epithelial proliferation begins shortly after implantation, and soon short thick cellular processes extend from the antimesometrial side of the lumen whereas long branching cords penetrate the decidua basalis mesometrially. The function of this structure is unknown.