Introduction 3 



growth of a leaf or a flower from a tiny primordium, especially when this 

 is speeded up to our eyes by time-lapse photography. Every step is co- 

 ordinated with all the others as though a craftsman were molding it ac- 

 cording to a plan. Within the whole, the cells and other subordinate 

 parts do not develop independently but all are knit together into an 

 organized system. 



How all this is accomplished and a specifically formed organism pro- 

 duced is not yet understood, although specific parts of the process are 

 now well known. Most metabolic activities are yielding to biochemical 

 analysis; students of gene action find that specific substances are produced 

 by specific genes, and the nucleic acids, with their remarkable properties, 

 are recognized as being at the very foundation of life itself. How all the 

 various metabolic and developmental activities are related in such an 

 orderly fashion, however, and proceed without interference or confusion 

 so that, step by step, an organism is produced poses a problem of a very 

 different kind. Relations, not chemical changes, are the facts to be ex- 

 plained. The problem must be approached experimentally but one should 

 recognize that this may require the development of techniques and ideas 

 not yet explored. 



The biological science concerned with this dynamic and causal aspect 

 of organic form is evidently different from either morphology, physi- 

 ology, or embryology, though partaking of all three. It deserves a 

 name of its own. The Germans usually call it Entwicklungsmechanik, a 

 name proposed by Wilhelm Roux. This great zoologist is looked upon as 

 the father of the science of zoological morphogenesis. He founded the 

 Archiv fiir Entwicklungsmechanik der Organismen, a journal which now 

 occupies 16 feet of library shelf and contains a vast amount of material, 

 chiefly on the animal side. Elsewhere this science has often been termed 

 experimental morphology or experimental embryology. Rritish biologists 

 sometimes refer to it as causal morphology. In recent years it has generally 

 been given a more appropriate name than any of these— morphogenesis. 

 The derivation of this word is obvious— the origin of form. Who first used 

 it is not certainly known but Ernst Haeckel employed the cognate form 

 morphogeny (Morphogenie) in 1859. Some have employed this term in 

 a strictly descriptive sense, essentially as synonymous with developmental 

 morphology. More commonly and properly, however, it includes, in addi- 

 tion to a discussion of purely descriptive facts as to the origin of form, a 

 study of the results of experimentally controlled development and an 

 analysis of the effects of the various factors, external and internal, that 

 determine how the development of form proceeds. In other words, it 

 attempts to get at the underlying formativeness in the development of 

 organisms and especially to reach an understanding of the basic fact of 

 which form is the most obvious manifestation— biological organization 



