184 ROYAL SOCIETY OF CANADA 



gemmules derived from the cells of an atrophied organ in a parent would 

 thus account for the appearance of atrophy of the organ in the offspring 

 while those from an organ whose size has been enhanced by use deter- 

 mine the special development of the organ in the next generation. 



'As already stated this theory met at the outset trenchant criticism. 

 It was pointed out that a single ovum of an adult animal, a vertebrate, 

 for example, would have to contain many times more gemmules than its 

 cubic capacity provided for unless they were of exceedingly minute size, 

 that is no larger than simple molecules, in which case they could hardly 

 be representative of the cells giving origin to them. There was also the 

 difficulty of understanding how the germinal cells received only the same 

 number of gemmules from each individual part of the body, for the 

 gemmules of the tissues and cells adjacent to the growing germinal cells 

 would reach the latter in greater numbers than those from more distant 

 parts. To explain this one would have to invoke the idea of a special 

 affinity on the part of the germinal cells for gemmules from the more 

 remote structures of a degree in proportion to the remoteness, or to 

 postulate the existence of some unknown directive force, not only guid- 

 ing the course of the gemmules, but arranging them in the germinal cells 

 in such an order that alterations in the organs of either or both of the 

 parents would be reproduced in the offspring. To postulate such an 

 affinity on the part of the germinal cells or such an unknown force in an 

 explanation of heredity merely substitutes one difficulty for another. 

 The most damaging criticism, however, came fifteen years after the 

 promulgation of the theory, In 1883 Weismann denied in toto the 

 validity of the evidence on which the belief in the inheritance of acquired 

 characters was based. He was not the first to do so for Kant ridiculed 

 the belief as baseless, and His about twelve years before Weismann also 

 disputed the facts, but Weismann was the first to direct attention to the 

 cardinal point in the discussion, and it is his great merit that he has 

 placed the subject in a wholly new light. His analysis of the facts which 

 have been adduced in support of the inheritance of mutilations and other 

 artificially produced structural alterations showed quite unmistakably 

 that very many of these are not to be regarded as trastworthy and that 

 others may be explained as not due to inheritance of such characters in 

 any respect. In consequence of his efforts and teaching a school of 

 biologists has developed during the last twenty-five years which regards 

 all the evidence advanced in support of the belief in the inheritance of 

 acquired characters as absolutely baseless. 



It is this attitude of mind amongst biologists generally that doomed 

 the theory of Pangenesis. If acquired characters, are not transmitted 

 gemmules of the character demanded by the theory are not needed and 



