ELEMENTARY MORPHOGENESIS 45 



would seem to us probably so great that all the similarities 

 would seem to disappear. 



But there are similarities, nevertheless, in all development, 

 and we shall now proceed to examine what they are. As 

 a matter of fact, it was especially for their sake that we 

 studied the ontogeny of a special form in such detail ; one 

 always sees generalities better if one knows the specific 

 features of at least one case. What then are the features 

 of most general and far-reaching importance, which may be 

 abstracted from the individual history of our sea-urchin, 

 checked always by the teachings of other ontogenies, includ- 

 ing those of plants ? 



THE FIRST STEPS OF ANALYTICAL MORPHOGENESIS 



If we look back upon the long fight of the schools of 

 embryologists in the eighteenth century about the question 

 whether individual development was to be regarded as a real 

 production of visible manifoldness or as a simple growth of 

 visibly pre-existing manifoldness, whether it was " epi- 

 genesis " or " evolutio," there can be no doubt, if we rely 

 on all the investigations of the last hundred and fifty years, 

 that, taken in the descriptive sense, the theory of epigenesis 

 is right. Descriptively speaking there is a production of 

 visible manifoldness in the course of embryology : that is 

 our first and main result. Any one possessed of an average 

 microscope may any day convince himself personally that 



it is true. 



In fact, true epigenesis, in the descriptive sense of the 

 term, does exist. One thing is formed " after " the other ; 

 there is not a mere " unfolding " of what existed already, 



