THE GENESIS OF LIVING ORGANISMS 221 



to the individual cells, without the entire organ-system taking 

 part in the digesting activity ; for the system of organs is 

 at that time busy with its own development. 



The provision of food is regulated according to the re- 

 quirements of the shaping process, and so is under the control 

 of the rule of genesis. 



This state of things changes as soon as the framework is 

 completed and the function of the fully-formed subject begins. 

 The majority of animals at this stage are not yet full-grown, 

 but need a longer or shorter time before they reach their 

 definitive size. Indeed, there are animals, such as some 

 kinds of fish, that are never full-grown, but go on increasing 

 in size to the end of their lives. 



As Wessely has shown, growth during this period no longer 

 obeys the rule of genesis, but the rule of function. By operat- 

 ing in various ways on one of the lenses in young rabbits, 

 Wessely succeeded in so influencing the regeneration of the 

 lens that the new one was sometimes smaller and sometimes 

 larger than that of the normal eye. And it appeared that the 

 growth of all the tissues of the eye, and even of the skull- 

 bones that form the orbit, directed itself with reference to this 

 new lens. Consequently the full-grown rabbit had in the one 

 case a larger eye than the normal, and in the other a smaller. 



If we compare this result with what Braus found after 

 reducing the germinal area for the acetabulum, the radical 

 difference between the two must be obvious to every one. 

 So long as function has not begun, the immediate environment 

 is not in the least concerned as to the size of the developing 

 member ; but if the framework has come under the sway 

 of the rule of function, the whole environing region must, in 

 growing, adapt itself to the growth of the regenerating 

 structure, and keep pace with it. 



Before the critical point has been reached, the impulses 

 governing growth follow exclusively the general rhythm of 



