2 Introduction 



interesting parallels between the two. In a study of form in organic de- 

 velopment the biologist has the great advantage of dealing with a process 

 that is going on under his eyes and is thus susceptible to experimental at- 

 tack. An organism is not static but displays a continually unfolding 

 series of changes during its life. It has been well described as a "slice of 

 space-time." As knowledge about organic development increased, biol- 

 ogists came to realize that development is not only an orderly unfolding 

 but that in this process all parts of the growing individual are closely 

 correlated with the rest so that an organized and integrated system, the 

 organism, is produced. Differences in rate of growth and in character of 

 the structures developed are evident, but these various changes do not 

 occur independently. They keep in step with one another. When form 

 changes, it does so in a regular and predictable fashion. Still more sig- 

 nificant, the experimental embryologist is able to show not only that these 

 relationships are to be seen in normal development but that they per- 

 sistently tend to be restored if development is disturbed. An organism is 

 an essentially fluid system through which matter is continually moving 

 but which nevertheless maintains a constant form much as does a candle 

 flame or a waterfall. 



In the various physiological activities of the living organism there is 

 evident the same coordination so manifest in bodily development. What 

 occurs in an individual is not simply a series of unrelated metabolic 

 processes, but these are tied together in such a precise fashion that the 

 life of the organism is maintained in a steady state. Just as the normal 

 progress of development tends to be restored if it is disturbed, so the 

 normal state of physiological organization tends to be maintained at a 

 constant level. This regulatory process of homeostasis is recognized as 

 one of the major facts of physiology. 



Organic form is thus the visible expression of an inner relatedness 

 characteristic of life at every level. This can be most simply designated 

 as biological organization and is the most important problem that con- 

 fronts students of the life sciences. Form may be thought of not only as 

 the soul of natural history in the sense that it provides a measure of evo- 

 lutionary relationship but as the soul of all biology, since it provides the 

 most obvious and easily accessible manifestation of the basic character- 

 istic of life. 



Biological organization is to be seen most distinctly in bodily develop- 

 ment. It is obvious that, to produce an individual with a specific form 

 and structure, growth must be more rapid in some directions than in 

 others and must form tissues and organs of different character in different 

 places. Embryology has shown how precisely the activities in one part of 

 the developing individual are related to those in every other part. Few 

 happenings in nature are as fascinating to watch as the unfolding and 



