PREFACE TO 

 THE SECOND EDITION 



Cytology began by describing what sort of things cells were. 

 It continued by inferring what things happened inside them. Its 

 last and longest task is to discover why these things happen. 

 The purpose of this book is to explain what questions are raised by 

 this last kind of enquiry, and how some of them may be answered. 



The first stage of simple description survives in cytology, as it 

 must needs survive until it has embraced the whole diversity of 

 living organisms. The different stages of development therefore 

 continue side by side to-day. None the less the distinction of 

 method between the old and the new is profound. To many it is 

 so profound as to be unintelligible. Finding out why things happen 

 in the cell is an entirely different matter from finding out how they 

 happen. The one problem is a matter of skill and common sense. 

 The other takes us into a new element. We are plunged into 

 inferences, often speculative inferences, which connect mechanics, 

 physiology and genetics. We find that the cell is part of an inter- 

 locking system of growth and reproduction, heredity and variation. 

 Everything that happens in the cell is related to everything else 

 that happens in the organism, or indeed has happened in its ancestors. 



It is impossible at one and the same time to deal with all these 

 dialectical relationships. I can describe only those that seem 

 to me most important at the moment. In the first edition I took 

 the evolutionary point of view as being the most neglected and most 

 necessary. I devoted a last chapter to reconsidering our knowledge 

 of the cell from this point of view ; I attempted to show cell- 

 processes as the products of an evolution of the genetic system 

 which in changing adapts itself to its own requirements. This 

 theory can now be applied with greater rigour in the light of our 

 increasing knowledge of genotypic control and in the light of the 

 comparisons and experiments embodied in the chiasmatype theory 



