Pkoblems and Concepts of Evolution 19 



On the other hand, there are characteristics which are repeated in the next and 

 following generations, frequently for long periods of time ; these are, therefore, 

 asserted to be " germinal." 



We have been too lenient with the Weismannian dogma and the criterion it 

 establishes, that because a character does not appear in the next generation it is 

 not a product of germinal origin ; but there is no longer any doubt that there are 

 conditions in the population that are entirely the product of gametic factors 

 which may not appear in successive generations, due solely to the fact that the 

 right combination of factors is not made. A further fault at the present moment 

 is the assumption that because a character is not " inherited " by the progeny 

 it therefore is somatic in character, and while I do not doubt the existence of 

 modifications which are purely somatic in character and are, on the basis of 

 present knowledge, hardly to be expected to be of inheritable kind, nevertheless 

 the backward application of this test is not justified, and I shall be able to show 

 later that there are characters which " do not appear to be inherited," which are 

 purely germinal in origin. Furthermore, it is shown in some of this work that 

 there are conditions appearing in populations which would be characterized by 

 De Vries as fluctuations, and which are not capable of fixation in permanent 

 form and are not inheritable, which are not somatic, but germinal, due to the 

 presence in the gametic system of gametic factors occupying positions or rela- 

 tions such that their action is to produce this irregularity. In other words, they 

 act as impurities in the gametic system in the same way that impurities may act 

 in non-living physical systems. 



INHERITANCE. 



Inheritance is also simply a collective term descriptive of the reaction of 

 gametic agents and their behavior through a series of generations, and the 

 results which may follow from the combination of specific gametic factors. It 

 is hardly possible at the present moment to distinguish between the phenomena 

 called " variation " and " heredity " ; and operations often characterized 

 heredity are distinctly important in the production of heterogeneity in natural 

 populations. 



These two groups of phenomena, heterogeneity and heredity, are the basis, of 

 course, upon which evolution works, and present problems are, therefore, of two 

 general kinds : First, by means of the principles which have been developed in the 

 last fifteen years, there must be undertaken an extensive and accurate analysis 

 of the gametic constitution of organisms in terms of their component factors 

 and determining agencies; secondly, with this knowledge gained and with 

 materials of known gametic constitution available, to analyze the phenomena of 

 heterogeneity, undei? the controlled conditions of laboratory experimentation 

 and also in organisms in nature. In combining these two I have attempted to 

 trace in some degree the significance of heterogeneity in several species of these 

 organisms, and this effort, I believe, gives a clear insight into the real signifi- 

 cance of natural diversity and the potentialities present in natural species for 

 the production of divergent groups, and through this means perhaps there is a 

 new method of attack upon the problem of origin of species. Actual evolu- 

 tion operations of course center in and around the processes concerned in the 

 production of heterogeneity and the operations which are termed collectively 

 " heredity." Everything that ever has been or ever shall be in the evolution of 



