vi Translator's Preface 



fluous. But it contained the germ of de Vries's intra- 

 cellular pangenesis, the direct progenitor of the mutation- 

 theory. It was primarily because of this genetic rela- 

 tionship, together with the masterful way in which the 

 hypothesis is developed, and the accompanying wealth 

 of illustration, that the little German volume, here done 

 into English, was deemed worthy of translation at the 

 present time. 



As those who have followed the more recent liter- 

 ature of theoretical biology well know, Delage has argued 

 against accepting any of the micromeric theories of the 

 structure of protoplasm. His argument is based upon 

 the idea that, by the law of probabilities, no one can ever, 

 by pure imagination, correctly conceive of the ultimate 

 structure of protoplasm in detail. Kellogg 3 cites this 

 criticism of Delage as "a sufficient reason against accept- 

 ing any one of these highly developed theories of the 

 structural and functional capacity of invisible life units." 

 Possibly this is correct, but that depends upon what the 

 given hypothesis is to be accepted for. Of course no 

 unverified hypothesis should be accepted for truth. As 

 soon as the hypothesis can be so accepted it ceases to be 

 a hypothesis, or even a theory, and passes into the rank 

 of ascertained fact. 



But that the argument of Delage can be advanced as 

 a reason for rejecting any hypothesis, not inherently im- 

 probable or absurd, as a working hypothesis, a point of 

 departure for further experiments, serving to orient a 

 whole body of investigators, seems to me entirely to miss 

 the point of the purpose of a hypothesis. Hypotheses 

 are not statements of truth, but instruments to be used 

 in the ascertainment of truth. Their value does not de- 



3 Kellogg, V. L., Darwinism To-day, p. 223. New York, 1907. 



