[Genesis of islands in the human placenta]

A fetal origin of the isalnds was supposed after light microscopical observations, investigated especially on young placentas. Electron microscopical examination confirm this supposition. The following facts prove, that the islands are products of the trophoblast: 1. The development of Langhans-cells to the differentiated cytotrophoblast, passing the state of the transitional cell type - I have called the differentiated cytotrophoblast "trophocyte". 2. The linkage of the trophocyte to the syncytiotrophoblast of the islands by desmosomes. 3. Definite morphological differences between the trophocytes and the decidual cells. 4. The absence of connective tissue and vessels in the islands.