" 1895.) Search for the Unknown Factors of Evolution. 421 
of it has recently come from Driesch® in his implication that 
there is a factor not only unknown but unknowable! 
Theoretically neither of these five hypotheses of the day ex- 
cludes the others. They may all codperate. The role which 
each plays, or the fate of each in the history of speculation 
largely or wholly depends upon the solution of the problem of 
the transmission or non-transmission of acquired variations 
and after all that has been written on this question this must 
be regarded by every impartial observer as still an open one. 
We are far from finally testing or dismissing these old fac- 
tors, but the reaction from speculation upon them is in itselfa 
silent admission that we must reach out for some unknown 
quantity. It such does exist there is little hope that we shall 
discover it except by the most laborious research ; and while 
we may predict that conclusive evidence of its existence will 
be found in morphology, it is safe to add that the fortunate 
discoverer will be a physiologist. 
THE ANALYSIS OF VARIATION. 
After this introductory survey let us consider as another 
outcome of the controversy that Variation and the related 
branch of research, Experimental Evolution, are now in the 
foreground as the most important and hopeful of the many 
channels into which the inductive tests of known or unknown 
factors may be turned. Let us make an honorable exception 
of those reactionists, such as Bateson and Weldon, who have 
instituted an exact investigation into the laws of Variation. 
How shall the study of Variation be carried on? I totally 
differ at the outset from Bateson in the standpoint taken in the 
introduction of his work, that the best method of starting such 
an investigation is in discarding the analysis which rests upon 
the experience as well as the more or less speculative basis of 
past research. There is little clear insight to be gained by 
considering variations en masse, and in this lecture I shall put 
forth some reasons why this is the case as well as some prin- 
5 Analytische Theorie der Organischen Entwickelung. Leipsic, 1894. 
*W. Bateson: Materials for the Study of Variation, London, 1894. 
