8o PROBLEMS OF GENETICS 



reformation, and especially the forking of the old ridges where 

 they join the new ones, are curiously reminiscent of the irregu- 

 larities of segmentation seen in regenerated structures. The 

 value of the considerations adduced in the chapter is, I admit, 

 very small. The utmost that can be claimed for them is that 

 mechanical segmentations, like those seen in ripple-mark, or 

 in Leduc's osmotic growths, show how by the action of a contin- 

 uous force in one direction, repeated and serially homologous 

 divisions can be produced having features of similarity common 

 to those repetitions by which organic forms and patterns are 

 characterised. The analogy supplies a vicarious picture of the 

 phenomena which in default of one more true may in a slight 

 degree assist our thoughts. It suggests that the rhythms of 

 segmentation may be the consequence of a single force definite 

 in direction and continuously acting during the time of growth. 

 The polarity of the organism would thus be the expression of 

 the fact that this meristic force is definitely directed after it has 

 once been excited, and the reversal seen in some products of re- 

 generation suggest further that it is capable of being reflected. 

 This polarity cannot be a property of the material, as such, 

 but is determined by a force acting on that material, just as the 

 polarity of a magnet is not determined by the arrangement of its 

 particles, but by the direction in which the current flows. 



To some it may appear that even to embark on such discussions 

 as this is to enter into a perilous flirtation with vitalistic theories. 

 How, they may ask, can any force competent to produce chem- 

 ical and geometrical differentiation in the body be distinguished 

 from the "Entelechy" of Driesch? Let me admit that in this 

 reflexion there is one element of truth. If those who proclaim 

 a vitalistic faith intend thereby to affirm that in the processes 

 by which growth and division are effected in the body, a part is 

 played by an orderly force which we cannot now translate into 

 terms of any known mechanics, what observant man is not a 

 vitalist? Driesch's first volume, putting as it does into intel- 

 ligible language that positive deduction from the facts es- 

 pecially of regeneration should carry a vivid realisation of this 

 truth to any mind. If after their existence is realised, it is 



