No. 530] PURE LINES IN STUDY OF GENETICS 89 



painful surprise, for like Pearson I find it impossible to 

 construct for myself a "philosophical scheme of evolu- 

 tion" without the results of selection and I would like to 

 see what I believe must occur. It is therefore with some 

 pleasure that I am able to record for Paramecium this 

 extensive operation of selection among the diverse exist- 

 ing lines, and particularly in this extensive production of 

 new combinations at conjugation, with cancellation of 

 many of the combinations. It would seem that the 

 diverse genotypes must have arisen from one, in some 

 way, and when we find out how this happens, then 

 such selection between genotypes will be all the selection 

 that we require for our evolutionary progress. What I 

 hope, therefore, is that some one on our program, more 

 fortunate than myself, will be able to record seeing the 

 actual production of two genotypes from one, or the 

 transformation of one into another, by selection, or in any 

 way whatever. 



Yet even if this is done, we shall make the greatest 

 possible mistake if we therefore conclude that the exist- 

 ence of genotypes is unimportant, and throw the matter 

 aside ; for work with a mixture of unknown genotypes will 

 always give confused and ambiguous results, whose signi- 

 ficance no one can know. If on the other hand we work 

 with single genotypes, or with known combinations of 

 them, we shall understand what our results mean. And 

 this applies to work in other fields of biology as well as to 

 genetics. 



