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mate causes demonstrated to a degree which had not been pre- 

 viously attained. A scientific theory is like an organism, it grows 

 and it may also propagate itself, and all the theories of evolution 

 from Lamarck to de Vries, and those that will follow, will them- 

 selves be an example, as it were, of the principle that they teach. 

 A theory which starts life an intellectual pigmy, may develop, 

 if it have the vitality, into a veritable intellectual colossus, and, 

 after it has run its course, may leave behind its offspring. It is 

 not a cause of reproach but rather of congratulation that the 

 scientific theory of to-day may be discarded to-morrow, for no 

 theory will be abandoned until a better one has been brought 

 forward to take its place, one which can explain the facts in a 

 way more satisfying to the human mind. Change in such a case 

 is progress, and since science must of necessity be always pro- 

 gressing so also must it be always changing. 



To those who are conversant with the problems connected 

 with the origin of species, it must be obvious that this consider- 

 ation of the subject does not cover the whole ground ; so obvious, 

 indeed, that perhaps it is unnecessary for me to remark that it is 

 not intended to. There are other theories to be considered and 

 other equally important matters that are more or less interwoven 

 with any one theory of the evolution of new forms. Thus no 

 reference has been made to Mendel's researches on heredity, or 

 the way in which they touch upon the de Vries Theory. This 

 has been omitted purposely, for while the results of Mendel's 

 original experiments in the breeding of peas might be cited at 

 length, I doubt if an apter or more significant example could be 

 found than the one which Professor Wilson used, and as Pro- 

 fessor Wilson himself said, the explanation while not abstruse is 

 one that requires considerable preparatory consideration. The 

 Mutation Theory has been developed more in detail, as repre- 

 senting a type of research. Being one of the latest and most 

 important contributions to biological science, and being also 

 entirely germane to the subject in hand, it has seemed proper to 

 devote some time to its consideration. At many points do the 

 fields of modern botany and modern zoology touch, but perhaps 

 it is nowhere so evident as in great problems like these. Here 



