CHAPTER X. 



THE PROBLEM OF ORGANIC DEVELOPMENT— FACTS AND THEORIES. 1 



"Die allegemeinen Probleme gehoren doch zum Wesentlichen jeder Wissenschaft, und die 

 allegemeinen Erkenntnisse sind die Krone unseres Wissens." — Paul Jensen, Organische Zweck- 

 massigkeit, page vii. 



If all branches of biological research may be said to have a common goal, and 

 if the present trend of theories, methods, and interests in morphology and physi- 

 ology has real prospective significance, then we have not far to look for a proximate 

 definition of that goal. Variously aimed as are our many strivings, they appear to 

 me to have a common focal point in a comprehensive understanding of the nature, 

 laws, and limits of organic development. 



Development is the one word that seems to me to best circumscribe the more 

 general problems of biology. It is also the one word that best emphasizes the 

 essential unity of ontogeny and phylogeny. These two terms have been used as 

 if they stood for two distinct series of phenomena, when in reality they apply to 

 one and the same series. The misconception is far-reaching and fruitful in mystifi- 

 cation, as the never-ending controversies over the biogenetic law well illustrate. 

 These controversies have turned on the question of the causal relation affirmed to 

 exist between ontogeny and phylogeny, the latter being supposed to furnish a causal 

 explanation of the former. 



As a clear apprehension of this law is of crucial importance in the interpretation 

 of such phenomena as I have to present, and as an examination of its contents will, 

 I think, bring us somewhat nearer to the fundamental problem of organic develop- 

 ment, let us see if we can get at its essential truth. 



As all know, it is to Professor Haeckel that we are indebted for the name and the 

 current formula of this law. Professor Haeckel's formula, now nearly half a century 

 old, runs thus: "Ontogenesis is a brief and rapid recapitulation of -phylogenesis." 



Phylogeny is viewed as the primary fact upon which ontogeny is causally 

 founded, being conditioned by heredity and adaptation. Now, we must admire 

 the genius that can take the problem of development as Haeckel found it and so 

 concisely and luminously state the great riddle in its fundamental facts and cause. 

 Of course we do not forget that before the appearance of Haeckel's "General Mor- 

 phology" the greater minds in biology for more than half a century had been moving 

 toward such a formula. The whole grand procession, led by such men as Kiolmeyer. 

 Geoffroy Saint Hilaire, Lamarck, Meckel, Von Baer, Johannes Muller, Louis Agas- 

 siz, Vogt, and last, but not least, Darwin and Fritz Muller, must be said to have a 

 voice in Haeckel's delivery. 



The progress of bilogy since 1866 has raised an increasing number of critics of 

 the biogenetic law, but they have not seriously weakened the general conviction 

 of its validity. 



1 An address before the Seventh International Zoologieal Congress. Boston Meeting. 11107. No part of this address 

 (SS 13) has hitherto been published. A few pages of a manuscript (Z 10, on the Geopelia cuneata experiment) written 

 in the same year on a wholly similar subject has also been included. — Ed. 



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