Comparing the placenta from one species to another can be a challenging task. On one
hand, the gross anatomy of the placenta is at least superficially rather different among
different species (Wooding and Flint, 1994). To complicate matters, even where analogous
cell types exist, different names are often used to describe them in different species. The
temptation is to either give up or assume that the placenta evolved independently into very
different structures in different mammals. Although the differences are certainly interesting, a …