Reprinted from the Journal of th e Washington Academy of Sciences 

 Vol. VII, No. 10, May 19, 1917 



GENETICS. — Observed changes in hereditary characters in re- 

 lation to evolution. 1 H. S. Jennings, Johns Hopkins Uni- 

 versity. 



The problem of the method of evolution is one which the bi- 

 ologist finds it impossible to leave alone, although the longer 

 he works at it, the farther its solution fades into the distance. 

 The central point in the problem is the appearance, nature, and 

 origin of the heritable variations that arise in organisms; the 

 changes that occur in the hereditary constitution. I have for 

 a long time been studying the appearance of heritable variations 

 in certain lower organisms. Having satisfied myself as to the 

 nature of the variations that arise in the creatures that I have 

 studied, I have looked about to see what other workers have 

 found; and to determine whether any unified picture of the 

 matter can be made. Can we bring these facts which experi- 

 mental work has brought out into relation with the method of 

 evolution? Can we say that they exclude any particular theory? 



1 A lecture delivered before the Washington Academy of Sciences, March 15, 

 1917. 



