CHAPTER VIII 

 GENERAL PRINCIPLES OF MORPHOGENESIS 



THROUGHOUT the preceding descriptions and interpretations, 

 some general morphological principles are implicit. Since these 

 are moot questions, it is fitting that these assumptions be explicitly 

 stated and clarified. Several years ago in a discussion of the mor- 

 phogenesis of the brain ('33a) , some of these principles were critically 

 examined, and a part of what follows is condensed from that essay. 



MORPHOGENIC AGENCIES 



A century and a half ago the German Naturphilosophie elaborated 

 the mystic and poetic conception of an archetypical form, which was 

 popularized by Oken and Goethe and culminated with Sir Richard 

 Owen and Louis Agassiz. As Professor Owen wrote in 1849: "The 

 archetypal idea was manifested in the flesh under diverse such 

 modifications, upon this planet, long prior to the existence of those 

 animal species that actually exemplify it." These geistige Krcifte were 

 conceived as enduring morphogenic agencies which shape the course 

 of all animal and plant differentiation. 



After the publication of Darwin's Origin of Species in 1859, a new 

 school of morphologists arose under the leadership of men like Gegen- 

 baur, Haeckel, and T. H. Huxley, the guiding principle being a search 

 for phylogenetic relationships as key factors in morphogenesis. The 

 mystic enduement of the earlier archetype was replaced by a sound 

 biological principle of progressive change effected by verifiable in- 

 ternal and environmental agencies. 



This conception of morphology as the visible record of phyloge- 

 netic history has stood the test of time. It is dynamic, not static; and 

 our search is for the natural agencies which have operated to produce 

 the observed modifications of form and correlated behavior during 

 the course of evolutionary change. This century of progress has, how- 

 ever, witnessed a curious relapse, with resurgence of the ancient pre- 

 dilection for rigid categories and artificial systems of logical analysis, 

 which yield in the end a formulation of inflexible, and therefore ob- 

 structive, morphological principles. Ancient and heritable patterns, 



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