INTRODUCTION 



Two lines of research have developed with surpris- 

 ing rapidity in recent years. Their development has 

 been independent, but at many stages in their progress 

 they have looked to each other for help. The study 

 of the cell has furnished some fundamental facts 

 connected with problems of heredity. The modern 

 study of heredity has proven itself to be an instrument 

 even more subtle in the analysis of the materials of 

 the germ-cells than actual observations on the germ- 

 cells themselves. 



In the following chapters it has been my aim to point 

 out, wherever possible, the bearing of cytological 

 studies on heredity, and of the study of heredity on the 

 analysis of the germinal materials. 



The time has come, I think, when a failure to recog- 

 nize the close bond between these two modern Hues of 

 advance can no longer be interpreted as a wise or 

 cautious skepticism. It seems to me to indicate rather 

 a failure to appreciate what is being done at present, 

 and what has been accomplished. It may not be desir- 

 able to accept everything that is new, but it is cer- 

 tainly undesirable to reject what is new because of its 

 newness, or because one has failed to keep in touch with 

 the times. An anarchistic spirit in science does not 

 always mean greater profundity, nor is our attitude 

 toward science more correct because we are unduly 



