ABSTRACTIn two groups of experiments the so-called ‘somite centres ‘were removed from chick blastoderms. Nevertheless, well-developed somites formed. It is concluded, therefore, that the ‘somite centres’ are not essential for somite formation. The same experiments, and others which are described, also provided evidence that somites can form in the absence of neural tissue. It is concluded, therefore, that neural tissue is not essential for somite formation. Experiments involving extirpation of the node confirmed the now generally accepted findings of various authors that neither the node nor the notochord are essential for the differentiation of somites. It is suggested that the regression movements may play a decisive rôle in influencing somite differentiation.