V GENERAL REFLECTIONS AND CONCLUSIONS 285 



frequently unite later on to form complex organs, and the 

 necessary co-ordination of these is a ' harmony of composition '. 



Such, in brief, is the idea worked out in the Analytiscke 

 Theorie. On this hypothesis development is an epigenesis; 

 it involves a superadditio partium, an increase of structure, 

 a creation of fresh form out of the simple cytoplasmic organiza- 

 tion of the egg, and the causes which operate in this process of 

 morphogeny are just that initial structure and the stimuli which 

 the parts respond to, stimuli which may proceed from the parts 

 themselves or from the world outside. 



These responses are primarily physico-chemical and only 

 secondarily structural, and they happen in accordance with 

 a pre-established harmony. Only in this sense can development 

 be described as evolution ; but this is not the evolution of the 

 preformationists of the eighteenth century, nor even that of the 

 school of Roux and Weismann, less gross, more subtle, but still 

 morphological; rather it is the realization of a form which is 

 physically and chemically predetermined, not structurally pre- 

 formed, in the simple organization of the germ. 



The hypothesis is worthy of the attention of every serious 

 embryologist. It is scientific in the strict sense of the word, for 

 in employing Herbst's suggestion to bring the events of onto- 

 geny into the category of physiological responses to stimuli it 

 gives meaning and precision to Hertwig's somewhat vague idea 

 of the ( mutual relations of the parts ', and makes thereby 

 a genuine effort to think the particular under the universal, to 

 bring the facts of embryology under wide general laws of 

 causation. 



Its chief weakness is at present lack of evidence ; the develop- 

 ment of every organ requires to be examined by the touchstone 

 of experiment before the theory can rise beyond the rank of 

 a working hypothesis. That, however, is the common lot of all 

 working hypotheses, and this one has certainly some counter- 

 balancing advantages. Its conception of the role of the nucleus 

 has been to some extent borne out by Boverr's recent researches 

 and adopted by their author, a conception which, as we have 

 observed before, is not irreconcilable with the facts of budding 

 and regeneration. Secondly, only the very simplest original 



