experimental embryology. Driesch elaborated the results from a fundamental angle in his investigation entitled The Localisation of Morphogenetic Processes. 2 The experiments cannot be described here. I shall merely identify the fundamental result in a way that immediately reveals its connection to our problem. The subsequent development of one cell-group of the embryo is determined in the context of the whole and in relation to this whole. Once this has occurred, the development proceeds independently of the environment in the direction that has already been laid down. Here we clearly see the breakthrough of the idea of the whole—wholeness as such as the determining factor. This is the principle result of Driesch's investigations, which was of decisive significance both for the problem of the organism in general and also for the problem of development. But it is a result that is no longer conclusive today, since it has been set upon a new basis through the equally outstanding investigations of Spemann which have turned the problem of animal development and the unity of the organism in a quite new direction.
Now for all its significance for the general problems of biology, this very insight of Driesch also represents a great danger. For it is only one step and, as always, a step taken within the modern problematic. For these experiments seemed to confirm the old conception of life, according to which the organism behaves in a purposive manner, and suggested that we must try and explain this purposiveness. Thus Driesch was driven by his experiments to adopt his biological theory, known as neovitalism, which is characterized by the appeal to a certain force or entelechy. This theory is repudiated in large measure by biology today. As far as biological problems are concerned, vitalism is just as dangerous as mechanism. While the latter does not allow the question of purposive behaviour to arise, vitalism tries to solve the problem too hastily. But the task is to recognize the full import of this purposive striving before appealing to some force which, moreover, explains nothing. Nevertheless, these concrete investigations, disregarding the philosophical theory which is bound up with them, have proved to be of decisive significance. The difficulties of Driesch's theory are not essential for our purposes. What is essential is simply the fact that the organism as such asserts itself at every stage of life of the living being. Its unity and wholeness is not the subsequent result of proven interconnections. Yet if we recall our definition of the essence of the organism (captivation), we can see that the organism is certainly grasped as a whole here, yet grasped in such a way that the animal's relation to the environment has not been included in the fundamental structure of the organism. The totality of the organism coincides as it were with the external surface of the animal's body. This is certainly not meant to imply that Driesch or other scientists have
2. H. Driesch, Die Lokalisation morphogenetischer Vorgänge. Ein Beweis vitalist. Geschehens (Leipzig, 1 899).