Placentation in an American mole, Scalopus aquaticus

In 1938 Mossman reported that epitheliochorial placentation occurred in an insectivore, the Eastern mole. This led to a radical change in his thinking about placental evolution, yet 40 years would pass before the appearance of a definitive description. Unpublished papers in the Mossman Collection at the University of Wisconsin Zoological Museum tell a fascinating story about this delay. The Scalopus material was studied by Mossman's graduate student, M.R.N. Prasad, who concluded that the placenta was initially endotheliochorial and that subsequent re-epithelialization of the uterus led to the definitive epitheliochorial condition. Mossman withheld publication of these findings pending electron microscopic studies. The definitive publication described the ultrastructure of the interhaemal region. Although based on a single specimen, this seemed to justify the conclusion that an epitheliochorial condition was maintained throughout gestation. These findings are discussed in relation to subsequent work on the European mole and current thinking about placental evolution.