Significance of the Available Evidence. 603 



further investigations on this point, and these should 

 not merely be concerned with new i)henoniena, but with 

 ihe testing of results already obtained ; for many instances 

 of discontinuous origin stand in need of more convincing 

 ])roof, and in other cases the progressive nature of a 

 process which is interpreted as a mutation is often subject 

 to doubt. In such investigations attention should be 

 ])aid to the question whether the hypothetical i)remuta- 

 tions may perhaps be prepared gradually, whilst tlie new- 

 character which has been so developed in secret, might 

 unfold suddenly. But it will take many years to decide 

 these points. 



Starting from general arguments Kolliker^ was 

 the first to insist on the importance of mutations against 

 Darwin^ indicating the process, which was then a purely 

 hypothetical one, by the name heterogenic development. 

 Others have expressed themselves favoral)ly with regard 

 to this view ; especially K. E. von Baer and Bronn, and 

 also Haacke, G. Pfeffer, Delage, Cunningham, 

 Wolff, Dreyer, Driesch, Emery- and many others. 

 This doctrine has of recent years found its strongest 

 cham])ion in Bateson, wdiose view^s I have already dealt 

 with above. Those authors too, wdio have made mono- 

 graphic studies of special genera and species have wel- 

 comed it; for instance Wittrock. in his study of Jlola, 

 inclined to the view that species have originated discon- 

 tinuously. Further, this doctrine is defended on purely 

 speculative grounds by many prominent biologists, amoni;- 

 whom I need only mention Von Hartm axx and also 

 Hamann and Ker.sten." On the zool(\gical side Ilr- 



^KoLUKER. Abhandl. Scnchcuh. GcscUsch., 1864. pp- 22y22(). 



^ Emery, Biolog. Centralblalt, 1893, No, 13. V- 7^3- 



^ See the careful and critical exposition in IT. Kkksten's Die 



