THE PRESENT POSITION OF CELL-THEORY. 239 



vital elements occur at all, those same elements which make 

 life possible and control assimilation and growth must also 

 be the agents in bringing about the phenomena of heredity. 

 I have shown that minute vital elements smaller than 

 cells cannot be believed to exist, and it is clear that the 

 phenomena of heredity cannot be explained by things 

 which have no existence. This is a sufficient answer to 

 those who would say that the phenomena of heredity are 

 such that we must make use of a hypothesis of minute 

 vital elements, which are at once the bearers of the vital 

 qualities and the bearers of the heritable qualities (the his- 

 toric properties if the expression is preferred) of protoplasm. 

 It is not true that a theory of heredity is impossible unless 

 such elements are postulated. Delage has brought forward 

 a theory of heredity which discards altogether the use of 

 hypothetical biophors. I pass no criticism on his theory, 

 favourable or unfavourable, but call attention to it merely 

 for the purpose of showing that a theory without biophors 

 is possible. It is no argument to say that the theories 

 based on ultimate vital units have largely extended our 

 knowledge of heredity. The Ptolemaic system of astronomy 

 largely extended men's knowledge of the movements of 

 the heavenly bodies, but it was not on that account a true 

 theory. 



Moreover, it will be hardly fair to twit me with the 

 fact that I renounce, for the present, an attempt to explain 

 the most complicated manifestations of life, for this is only 

 an essay, and makes no pretence to be the development of 

 a doctrine. 



It is not my present intention to frame hypotheses, not 

 because I undervalue the use of hypothesis, but because I 

 regard the first necessary step to be the formation of ideas 

 appropriate to the facts. 



Dr. Whitman has recently written quite a nice little 

 lecture on the subject of fact and theory, and has directed 

 it against myself in particular, winding up with a trenchant 

 paragraph to the effect that the claim to a monopoly of 

 fact reflects an arrogance which seems to be epidemic. 

 This homily is fortified by quotations from von Baer, 



