Introduction 3 



be detonated into an explosive, disordered, dis- 

 harmonious, and ultimately self -destroying over- 

 growth?" The factors which control these char- 

 acteristics of size, form, function, and rate of 

 development of living organisms, which maintain 

 at all times the proper balance among their parts, 

 and which, when disturbed, result in creatures of 

 abnormal type, constitute the materials of that 

 important branch of biological science which we 

 call ' ' morphogenesis. ' ' 



Science progresses in five main steps. First, 

 there is the observation of more or less evident 

 facts, their codification and analysis. Second, 

 there is the formulation of ideas and principles 

 based on these facts and their arrangement into 

 working hypotheses. Third, there is the develop- 

 ment of techniques for the testing of these hy- 

 potheses. Fourth, there is the acquiring through 

 use of these techniques of pertinent but less evi- 

 dent information, the verification, modification, 

 and refinement of these hypotheses, until they 

 themselves become facts. And fifth, there is the 

 integration of these latterly acquired larger facts 

 into the general picture. In the study of living 

 organisms, one of the early observed "facts" was 

 the ubiquity of those units which we call cells. 

 Information about cells, acquired by general ob- 

 servation, very early led to the formulation of the 



