Sinnott • Morphology as a Dynamic Science 



87 



may still be described by Darwin's 

 words, in a famous passage of the 

 "Origin," as the "ver)' soul" of natural 

 history. Let us examine the evidence 

 for this contention. 



The correlative mechanisms by 

 which an integrated living individual 

 is maintained are, of course, physiolog- 

 ical in character and are doubtless ulti- 

 mately resolvable into physical and 

 chemical processes; but their investiga- 

 tion from the point of view of physi- 

 ology alone is usually beset by such dif- 

 ficulties that substantial progress on 

 this front must wait until the necessary 

 experimental technique is much more 

 highly perfected than it is today. The 

 coordinating and integrating capacity 

 of protoplasm, however, is displayed 

 not only in those correlations of func- 

 tion which so excite our amazement 

 but also in the more familiar and no 

 less remarkable correlations of growth, 

 operative during the process of develop- 

 ment and resulting in the production of 

 those specific and constant shapes of 

 organ and body which are so charac- 

 teristic of living things. A fertilized egg 

 divides this way and that in such a pre- 

 cise manner that an embryo with two 

 cotyledons, a plumule and a hypocotyl, 

 definite and specific in form, are pro- 

 duced. From a tiny mass of undifferen- 

 tiated cells at a growing point are de- 

 veloped the primordia of organ after 

 organ in a perfectly regular fashion, and 

 each follows in its enlargement a defi- 

 nite pattern of growth. In all such cases 

 there is manifest in the clearest fashion 

 that coordinating control of which I 

 have spoken. Form is merely the out- 

 ward and visible expression, fixed in 

 material shape, of that inner organized 

 equilibrium which we are seeking to 

 understand. 



If it be admitted that our basic 

 problem can thus be approached most 

 simply and directly through the door 

 of morphology, then an investigation of 

 the factors which determine organic 



form assumes a major place in biolog- 

 ical science. That this importance is 

 coming to be generally recognized is 

 evident in the diversit)' of directions 

 from which developmental problems 

 in plants and animals are now being at- 

 tacked. Physiology has always regarded 

 correlative development as an integral 

 part of its domain, but in recent vears 

 this subject has assumed a steadily 

 growing importance, as witness the in- 

 tensive researches on hormones, orga- 

 nizers, metabolic gradients and mor- 

 phogenetic fields. Genetics is now 

 increasingly concerned with an attempt 

 to discover how genes control develop- 

 ment and thus produce the traits by 

 which they are recognized. Ecological 

 attack upon the problem of changes in 

 form through environmental factors 

 has been intensified by discoveries in 

 various fields. Even physicists and 

 chemists have been intrigued by de- 

 velopmental problems and have made 

 important contributions toward their 

 solution. 



In this diversified attack upon the 

 problem of the causes of the coordi- 

 nated developmental processes which 

 result in the production of organic 

 form, only a relatively minor part, 

 strangely enough, has been played by 

 those biologists who might have been 

 expected to be more interested in it 

 than any one else— the morphologists 

 themselves. With important excep- 

 tions, those botanists and zoologists 

 whose primary concern has been with 

 the form and structure of living things 

 have contented themselves with the 

 static and descriptive aspects of their 

 science rather than with its dvnamic 

 and developmental side. The reason for 

 this one-sided emphasis in morphology 

 is evidently a historical one. The form 

 of organisms has always fascinated 

 biologists. Its constancy in each species, 

 its almost infinite diversitv and the ex- 

 istence of underlying similarities in 

 form between groups of organisms have 



