Morphogenesis and fine structure of the near-term placenta of Talpa europaea: I. Endotheliochorial labyrinth.

Morphological studies of placentation of Talpa europaea confirm an antimesometrially orientated discoidal and chorioallantoidic placentome. This placentome, near term, shows a villous labyrinthine zone with interspersed haematomal areolae on its fetal side, a centrally located fetomaternal junctional zone, and a uterine gland zone towards the myometrium. As shown by light and electron microscopy the interhaemal membrane in the labyrinthine zone develops to an endotheliochorial placentation type. It consists of a prominent maternal endothelium, a distinct interstitial layer, which contains some endometrial debris and is interrupted by some endotheliochorial contact points, a bilayered trophoblast with a thin syncytial and a larger cytotrophoblastic component, and a small fetal endothelium. Disintegration of endometrial epithelium takes place at the areolar glandular mouths and in the junctional zone where a decidual cell reaction can also be observed, but no decidual cells become integrated into the labyrinth. In the spectrum from epitheliochorial to haemochorial placentation, Talpa europaea exhibits a less endotheliochorial type of placentation than is the case with carnivores.