INTRODUCTION 3 



placed within them, the germs of all subsequent 

 creatures. 



To reckon at their proper value the theory of 

 preformation, and, still more, the doctrine of en- 

 folded germs, the standard of appreciation must 

 not be the present range of our knowledge. They 

 must be viewed historically, in the light of the 

 knowledge of these days. 



Nowadays it is not so much pure reason as a 

 wider empirical knowledge of nature, with its con- 

 sequent transformation of ideas, that makes the 

 doctrine of enfoldment difficult. Abstract thought 

 sets no limit to smallness or greatness ; for mathe- 

 matics deals with the infinitely small and with the 

 infinitely great. So long as actual observation had 

 not determined the limits of minuteness in the 

 cases in question, there were no logical difficulties 

 in the doctrine of enfolded germs. The biology of 

 earlier centuries had not our empirical standard. 

 What appeared then to be a simple organic 

 material we have resolved into millions of cells, 

 themselves consisting of different chemical materials. 

 The chemical materials have been analysed into 

 their elements, and chemistry and physics have 

 determined the dimensions of the ultimate molecules 

 of these. It is only because the minute constitu- 

 tion of matter is no longer a secret to us that the 

 theory of germ within germ now touches the 

 absurd. 



It was very different in earlier days ; the acutest 

 biologists and philosophers were evolutionists, and 

 an epigenetic conception of the process of develop- 



