PREFACE. 9 



orate theory, on the basis of which we can propound 

 new questions, which will give rise in turn to new 

 facts, and thus will exercise a retroactive influence on 

 the theory, improving and transforming it. 



This is precisely what I have sought to accomplish 

 by my theory of Germ-plasm, as I stated in the Preface 

 to the book bearing that name. It was never intended 

 as a theory of life, nor, indeed, primarily, as a theory 

 of evolution, but first and above all as a theory of 

 heredity. I cannot understand, therefore, the animad- 

 version, that my theory in no way furthers our insight 

 into the mechanics of development. That is not its 

 purpose; in fact, it takes the ultimate physical and 

 chemical processes which make up the vital processes 

 for granted; and inevitably it is constrained to do 

 so. Its aim is to put into our hands a serviceable 

 formula by means of which we can go on working 

 in the field of heredity at any rate, and, if I am not 

 mistaken, also in that of evolution. To me, at least, 

 the newest results of developmental mechanics do 

 not seem so widely at variance with the theory of 

 determinants as might appear at first sight ; so far 

 as I can see, they can be quite readily made to har- 

 monise with the theory, provided only the initial stage 

 of the disintegration of the germ-plasm in the deter- 

 minant groups be not invariably placed at the begin- 

 ning of the process of segmentation, but be transferred 

 according to circumstances to a subsequent period. 

 The exact state of things cannot as yet be determined, 

 so long as the mass of facts is still in constant flux. 



In any event I still hold fast to the hope which I 

 expressed in the Preface to my Germ-plasm, that de- 

 spite the unavoidable uncertainties in its foundation 

 my theory would yet prove more than a mere work 



