CHAPTER XVIII 



TJIK I;KI;INI\'IN<;S OK CAUSAL MOKIMIOLOOV 



UNTIL well into the 'eighties animal morphology remained a 

 purely descriptive science, content to state and summarise 

 the relations between the coexistent and successive form- 

 states of the same and of different animals. No serious 

 attempt had been made to discover the causes which led to 

 the production of form in the individual and in the race. 



It is true that evolution-theory had offered a simple 

 solution of the great problem of the unity in diversity of 

 animal forms, but this solution was formal merely, and went 

 little beyond that abstract deduction of more complex from 

 simpler forms, which had been the main operation of pre- 

 evolutionary morphology. Little was known of the actual 

 causes of ontogeny, and nothing at all of the causes of 

 phylogeny ; it was, for instance, mere rhetoric on Haeckel's 

 part to proclaim that phylogeny was the mechanical cause of 

 ontogeny. 



Animal physiology, on its side, had developed in complete 

 isolation from morphology into a science of the functioning 

 of the adult and finished animal, considered as a more or 

 less stable physico-chemical mechanism. Since the days of 

 Ludwig, Claude Bernard and E. clu Bois Reymond, the 

 physiologists' chief care had been to analyse vital activities 

 into their component physical and chemical processes, and 

 to trace out the interchange of matter and energy between 

 the organism and its environment. Physiologists had left 

 untouched, perhaps wisely, the much more difficult problem 

 of the causes of the development of form. For all practical 

 purposes they took the animal-machine as given, and did 

 not trouble about its mode of origin. They held indeed 



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