Significance of the Available Evidence. 603 
further investigations on this point, and these should 
not merely be concerned with new phenomena, but with 
the testing of results already obtained ; for many instances 
of discontinuous origin stand in need of more convincing 
proof, 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 
paid to the question whether the hypothetical premuta- 
tions may perhaps be prepared gradually, whilst the new 
character which has been so developed in secret, might 
unfold suddenly. But it will take manv vears to decide 
tf m * 
these points. 
Starting from general arguments KoLLiKER 1 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 favorably with regard 
to this view ; especially K. E. VON BAER and BRONN, and 
also HAACKE, G. PFEFFER, DELAGE, CUNNINGHAM, 
WOLFF, DREYER, DRIESCH, EMERY 2 and many others. 
This doctrine has of recent years found its strongest 
champion in BATESON, whose views I have already dealt 
with above. Those authors too, who have made mono- 
graphic studies of special genera and species have wel- 
comed it ; for instance WITTROCK, in his study of Viola, 
inclined to the view that species have originated discon- 
tinuously. Further, this doctrine is defended on purely 
speculative grounds by many prominent biologists, among 
whom I need only mention VON HARTMANN and also 
HAMANN and KERSTEN. S On the zoological side Hu- 
1 KOLLIKER, Abhandl. Scuckcnb. Gescllsch., 1864, pp. 223-229. 
2 EMERY, Biolog. Centralblatt, 1893, No, 13, p. 723. 
3 See the careful and critical exposition in H. KERSTEN'S Die 
