THE DEVELOPMENT OF PATTERN 97 



skin trucks into lens and epidermis trucks. And so 

 on through all the sets of points, representing all 

 the organizers, till the final trains are made up 

 in the sidings, or, as we may say, the final organs are 

 developed from the embryo. 



In this model a competent tissue is analogous to a 

 truck just approaching a point. According as the 

 tissue is acted on or not acted on by an organizer, it 

 develops into this or that, and according as the 

 truck finds the points this way or the other, so it 

 runs down this siding or that. But in this com- 

 parison each point would act as an evocator and not 

 as an organizer, unless there is something to com- 

 pare with the individuators of the organizers. 

 Individuation by the primary organization centre 

 means determining what detailed structure the in- 

 duced organ will have, it means settling whether it 

 will be brain or spinal column, etc. In our model, 

 therefore, it means sorting a whole set of trucks into 

 their final sidings so that each siding gets the right 

 number. The first point, or primary organization 

 centre, can only do that if it is connected in some 

 way to all the other points by a system of levers so 

 that they all work together in a co-ordinated way. 

 The points alone do not provide a full analogy with 

 living organization centres, one must bring in the 

 set of individuating levers. 



The important thing to remember in this analogy 

 is that evocation, or the action of one point, can 

 happen to one single truck, that is to say, to one 

 small piece of tissue. But individuation, the har- 



