The development of the notochord of the albino-rat takes place in the period between 8 days 10 hours and 9 days 3 hours. The notochord appears as a thickness of the entoderm in the ventrally region of the antimesometrial cavity. At the stage of 8 days 10 to 14 hours p. c. there are observed differenciated processes of the primitive flattened entodermal epithelium to high cylindrical cells which form a plate. The closed structure of the basement membranes round the notochord of the rat, as it is observed lightmicroscopically reveals new aspects in connection of the frequent discussed supposition the notochord possibly to be a factor for the origin of other structures e.g. the somites. The developmental mode of the notochord of the albino-rat differs from that of the mouse.