Morphogenesis of the fetal membranes of the white‐tailed deer

Morphogenesis of the fetal membranes of the white‐tailed deer was studied throughout pregnancy. In placentomes, the long, branched, fetal villi occupied corresponding maternal crypts. The bases of the villi and the arching areas connecting them (arcades) were covered with high columnar cytotrophoblast, which apparently had phagocytosed material from the adjacent degenerating rims of the crypts. This arcade cytotrophoblast contained much glycogen and occasional mitochondria, free ribosomes, and pigment granules. Elsewhere, the columnar cytotrophoblast cells usually contained three to five rows of rod‐shaped mitochondria and other cytoplasmic organelles. Interspersed among them were numerous binucleate giant cells which usually contained peripheral lace‐like granular endoplasmic reticulum and many complex lipoprotein droplets. Cryptal epithelium, deep to the degenerate rims, was low columnar, had infranuclear osmiophilic lipid droplets, and sparsely distributed cytoplasmic organelles. The microvilli of cryptal and cytotrophoblastic epithelia interdigitated and appeared as a brush border under light microscopy. The microvilli and their PAS‐positive mucopolysaccharide material appeared capable of holding uterine and chorionic epithelia together during pregnancy. The placentomes were epitheliochorial, but showed “intra‐epithelial” capillaries. Interplacenomal uterine and cytotrophoblasitc epithelia resembled those of the placentomes. Their microvill were inundated by endometrial gland secretion (uterine milk). The cytotrophoblast contained pigment granules and much absorbed uterine milk. The amniotic epithelium showed short microvilli, complexly folded lateral plasma membranes, many desmosomes, abundant glycogen granules, foot processes and other cytoplasmic organelles.