GENERAL SUMMARY 



IT may not be out of place to state the general principles 

 of which use has been made apart from the concrete prob- 

 lems in which they appear. 



1. Growth and cell division. Organisms un/ler favorable 

 conditions accumulate energy which results in growth. 

 This increase of mass is counteracted by cell division, which 

 tends to reduce the size of individual organisms and to 

 increase their number. 



2. Surface unity and internal differentiation. The dis- 

 ruptive forces act more powerfully at the centres of organ- 

 isms than at the surface. The tendency to divide appears 

 first at two internal centrosomes and gradually extends out- 

 ward. This may be due to inadequate exits for waste prod- 

 ucts. The surface or envelope thus becomes stronger and 

 grows more rapidly than the interior. Folds result and 

 cause many subsequent complexities. The disruptive ten- 

 dencies in the interior are reduced by differentiations which 

 so complement each part that what is not utilized by the 

 one is food for the other. The amount of waste material is 

 thus reduced and the organism correspondingly strength- 

 ened. 



3. Double organisms. This internal tendency to divide 

 and to differentiate causes the higher organisms to become 

 practically if not in reality double. The differentiation of 

 mind from body and the bilateral divisions of the body are 

 instances of this tendency. 



211 



