GENERAL CONSIDERATIONS AND CONCLUSIONS 28 1 



middle of the anterior oblique surface, and the new tail arises from 

 the more posterior part of the posterior oblique surface. As an analy- 

 sis of this result has been already attempted in an earlier chapter, it 

 will not be necessary to go further into this question here. 



The development of a new part at right angles to an oblique sur- 

 face has also been described, and it has been pointed out that the 

 result appears to be due to the symmetrical development of the new 

 structure in the new part. This symmetry of the newly forming part 

 must be also counted as one of the properties of the organization. 



Finally, the mode of regeneration of a new, bifurcated tail in the 

 teleost, stenopus, shows that the new part may very early become 

 moulded into the characteristic form, and that the growth of the 

 different parts is regulated by the structure assumed at an early 

 stage. The new part does not grow out at an equal rate until it 

 reaches the level of the notch of the old tail, and then continue to 

 grow at two points to produce the bilobed form of the tail ; but 

 the bilobed condition appears at the very beginning of the develop- 

 ment. 



These illustrations give us nearly all the data that we possess at 

 present on which to build up a conception of the organization. That 

 we must fail in large part fully to grasp its meaning from these meagre 

 facts is self-evident. The main difficulty seems to lie in this, that 

 when we attempt to think out what the organization is we almost un- 

 avoidably think of it as a structure having the properties of a machine, 

 and working in the way in which we are accustomed to think of ma- 

 chines as working. The most careful analysis of the " machine 

 theory," as applied to the phenomena of development and of re- 

 generation, has been made by Driesch. It has been pointed out that 

 in his Analytische Theoric Driesch assumed that development is due 

 to " given " properties in the egg ; that each stage is initiated by some 

 substance contained in the egg acting on the stage that has just been 

 completed. That is, each stage is the condition of the following. 

 The "rhythm" of development is accounted for in this way. The 

 changes are described as due to chemical processes (including also 

 ferment actions). The nucleus is supposed to contain all the different 

 kinds of ferments that act, when set free, as stimuli on the protoplasm ; 

 but since the ferments are always set free at the propitious moment, 

 Driesch was obliged to assume that the cytoplasm acts on the nucleus 

 in such a way as to make it produce the proper ferment for the next 

 stage. Thus the cytoplasm first influences the nucleus, the latter 

 sets free a specific ferment that starts a new chemical change in the 

 cytoplasm, and the changed cytoplasm may then react again on the nu- 

 cleus, and a different ferment be set free, etc. Each change is there- 

 fore not only an effect of what has gone before, but the cause of the 



