Heredity in Protozoa 583 



have acted upon the' organism when it lived in connection with 

 individuals of past generations. We cannot hope, then, to study 

 the precise processes which have given rise to the particular com- 

 bination of characteristics which we find in Paramecium or the 

 dog or in any particular existing organism. All we can hope to do 

 is to study similar processes in progress, controlling and analyzing 

 them experimentally, till we work out the laws and principles of 

 their action. By application of what we thus gain to the results 

 of processes past, we may hope to reach an understanding of how 

 organisms have arisen. 



J Place of the Present Investigations in this Plan 



In taking up a study of these racial processes, we must first 

 learn as accurately as possible what occurs in the passage from 

 one generation to another; what resemblances and difi^erences are 

 normally found between members of succeeding generations, and 

 the like. In other words, we must have a knowledge of the nor- 

 mal phenomena of heredity and variation, such as is now being 

 acquired on a large scale in higher animals. When this is obtained 

 we may proceed to attempt to modify experimentally the processes 

 and their results — thus approaching the central problem: How 

 do inherited modifications arise .^ 



In such work, the relations found in the simplest organisms 

 deserve investigation. Here we have reproduction taking place 

 rapidly (a generation or more a day) and in the simplest forms. 

 I have therefore undertaken a study of the physiology of racial 

 processes in the Protozoa. Bearing more or less directly on this 

 matter we have already a large amount of most valuable work, 

 such as that by Maupas, Hertwig, Schaudinn, Calkins, Woodruff, 

 Enriques, and others. I have approached the matter however 

 from a different standpoint, setting the problems of inheritance 

 and variation definitely in the center of interest. This results in 

 somewhat different methods of attacking the subject. 



