SINCE the discovery by Bautzmann, Holtfreter, Spemann & Mangold (1932) that a diffusion of inducing substance takes place from the inductor into the competent reacting tissue, protein and ribonucleic acid have been favoured by candidates for the study of the nature of the inducing substance (see Brachet, 1960a, b). Recently Mangold, Tiedemann & Woellwarth (1956) studied the inductive capacity o...

Ultrasonic treatment of the tails of Triturus alpestris tadpoles, at intensities of 8 to 15 watts/cm(2), at 1 megacycle/sec., for 5 minutes, disrupted the epidermis and caused pycnosis in individual cells of the muscle and neural tube, but caused no damage to the notochord that could be detected by light microscopy. Electron microscopy showed that this ultrasonic treatment disordered nearly all...