THE AXIAL GRADIENTS IN HYDROZOA VI. EMBRYONIC DEVELOPMENT OF HYDROIDS

1. The axial gradient and its changes during development were demonstrated in Phialidium from oocyte to hydroid stage by differential susceptibility to various agents, differential reduction of KMnO4 and methylene blue and differential vital staining. Developmental stages of Gonothyraea and Stomotoca served as comparative material. The results of the different methods agree among themselves and with the observed facts of development.2. In Phialidium and Stomotoca the polarity of the oocyte is indicated by a gradient with high end at the free pole, low end at the attached pole. This gradient is directly related as regards direction to the differential exposure of the oocyte in the gonad and it is suggested that the polarity of the oocyte is determined by this differential exposure.3. The high end of the oocyte gradient becomes the apical pole of the egg at maturation and in early cleavage stages. During later cleavage a gradient is continuously present, but absence of landmarks makes complete demonstration ...