The Oviduct, Foetal Membranes, and Placentation in Hoplodactylus maculatus Gray.

Summary. The structure of the oviduct in the non‐pregnant lizard is described. The epithelium of the Fallopian tube consists of mucous‐secreting goblet cells and non‐secretory ciliated cells. Small glands, probably also mucous‐secreting, occur. There is a paucity of glands in the uterine segment of the oviduct, associated with the reduction of the shell. The uterine epithelium consists of ciliated non‐secretory and non‐ciliated secretory cells. The number of secretory cells increases during pregnancy. The vaginal epithelial cells are mostly ciliated, and glands are absent. The history of the placenta is described in six stages. As in other reptiles, a flattened cavity is formed in the yolk by the separation of a superficial layer of yolk. This is due to the growth of a layer of mesoderm into the yolk‐sac below the sinus terminalis, with the result that the nucleated yolk outside separates from the mesoderm layer. The isolated yolk‐layer becomes absorbed, disappearing first at the upper margin, which therefore moves down. There is a corresponding downward migration of the yolk‐cleft. The extra‐embryonic ccelom extends as the margin of the yolk‐layer moves down. Early in development dense syncytial yolk‐endoderm becomes organized round the yolk‐navel and functions as a yolk‐absorbing organ. The omphaloplacenta involves enlarged ectoderm cells round the lower part of the egg, lying opposite to enlarged secretory uterine epithelial cells. At the caudal end both layers are pleated and folded, but do not interlock. Eosinophil granules are secreted by the non‐ciliated uterine epithelial cells. The presence of blood‐vessels in the intra‐vitelline mesoderm provides easy transport for absorbed food material. The omphaloplacenta is diminished as the coelom extends, and finally the ectoderm cells bordering the remains of the isolated yolk‐layer become reduced. Enlarged cells remain at the caudal end ventrally until the end of gestation. The allantoplaeenta involves the; extreme reduction of the uterine epithelium over the dense capillary network, and the formation of an allantochorion in which the chorionic ectoderm and mesoderm above the allantoic capillaries become extremely thin, resulting in approximation of the maternal and foetal blood streams. There is no attachment between the allantochorion and the uterine wall. The allantois spreads round the yolk‐sac fairly early. The allantoplaeenta increases in extent until the birth of the young lizard. The influence of hormones on the formation of the placenta is suggested by cases in which the uterus on only one side is pregnant, but the other is correspondingly modified.