A simple method for separating the ectodermal (chorionic) and entodermal (allantoic) layers of the chorio-allantoic membrane has been devised. It consists of placing, unfolded, a membrane fragment on a rubber balloon filled with water; air is blown briskly upon the membrane by means of a rubber bulb until its shiny surface becomes dull; following this, a glass slide is applied on it, surface to surface, and then it is suddenly taken off, whereby the desired epithelial layer becomes attached to the glass surface. The microscopic observation of the layers thus individualized shows, on frontal view, their histological architecture, and the characteristic structural details of the constituent cells (cytoplasm, nucleus, nucleolus, cytoplasmic inclusions, mitochondria, stages in mitotic cell division, etc.).