26 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



process in the words of Wilhelm Eoux. We leave it an 

 open question in our present merely descriptive analysis, 

 whether there was already a " manifoldness," in an invisible 

 state, before development, or whether the phrase " pro- 

 duction of manifoldness " is to be understood in an absolute 

 sense. 



It has not always been granted in the history of biology, 

 and of embryology especially, that production of visible 

 manifoldness is the chief feature of what is called an 

 organism's embryology or ontogeny : the eighteenth century 

 is full of determined scientific battles over the question. 

 One school, with Albert von Haller and Bonnet as its leading 

 men, maintained the view that there was no production of 

 different parts at all in development, this process being a 

 mere " evolutio," that is, a growth of parts already existing 

 from the beginning, yes, from the very beginning of life ; 

 whilst the other school, with C. F. Wolff and Blumenbach 

 at its head, supported the opposite doctrine of so-called 

 " epigenesis," which has been proved to be the right one. 



To some extent these differences of opinion were only 

 the outcome of the rather imperfect state of the optical 

 instruments of that period. But there were also deeper 

 reasons beyond mere difficulties of description ; there were 

 theoretical convictions underlying them. It is impossible, 

 said the one party, that there is any real production of new 

 parts ; there must be such a production, said the other. 



We ourselves shall have to deal with these questions of 

 the theory of organic development ; but at present our 

 object is narrower, and merely descriptive. It certainly is 

 of great importance to understand most clearly that there 

 actually is a " production of visible manifoldness " during 



