2 54 REGENERA TION 



In the course of development each causal reaction brings about 

 not only chemically specific differences, and thereby makes possible the 

 introduction of new elementary processes, but the reaction also brings 

 about by this very means a lessening of the possibilities of the cell, 

 because each cell will now only respond to a more limited set of 

 causes. We may say that the elementary process is not only the 

 cause of the next change, but by virtue of its specific nature it is the 

 beginning stage of the future reactions. Development proceeds from 

 a few prearranged conditions, that are given in the structure of the 

 egg, and these conditions, by reacting on each other, produce new 

 conditions, and these may in turn react on the first ones, etc. With 

 every effect there is at the same time a new cause, and the possibility 

 of a new specific action, i.e. the development of a specific receiving 

 station for stimuli. In this way there develops from the simple con- 

 ditions existing in the egg the complicated form of the embryo. 



In this brief summary of some of the essential features of Driesch's 

 hypothesis, I have omitted some parts that seem to me to go beyond 

 the legitimate field of a scientific hypothesis, such, for instance, as the 

 causal harmony of the reactions ; and other parts have been omitted 

 because they are improbable in the light of more recent work. It 

 would not be difficult to show that many difficulties beset each stage 

 of the argument, or to show how slender a basis of fact there is to 

 support some of the hypotheses. In fact, Driesch himself has modi- 

 fied very greatly some of the views of his Analytische Theorie in his 

 later writings. The merits of the analysis should not be overlooked, 

 however, since it is one of the first philosophical attempts to show how, 

 in the light of recent discoveries, the process of epigenetic develop- 

 ment may receive a causal interpretation. Even if the argument 

 should break down, the hypothesis will remain an interesting contribu- 

 tion, opening the way to newer points of view in regard to the process 

 of development. In later papers, especially in those dealing with the 

 localization of morphogenetic processes, Driesch attempts to show that 

 certain experimental results demonstrate that there is a vitalistic prin- 

 ciple at work in the development of the organism from the egg, as 

 well as in the process of regeneration. He bases his argument on the 

 results of the experiment in which the gastrula of the sea-urchin egg 

 is cut in two, as described already on page 234. The archenteron has 

 not, at the time of the experiment, subdivided itself into its three char- 

 acteristic parts. The posterior piece, that contains the posterior part 

 of the archenteron (the anterior part having been removed with the 

 anterior piece), produces a new whole embryo of smaller size, in which 

 the archenteron is subdivided into three parts, that are in the same 

 proportion to each other and to the whole embryo as are the same 

 divisions of the normal archenteron. This proportionate formation of 



