Heredity in Protozoa 579 



tive in character, are found to be constituent parts of the organism, 

 yet they have not arisen in the way mentioned, but are "inherited" 

 from past generations. Such characteristics, in the field of be- 

 havior, are spoken of as reflexes, tropisms, instincts, etc.; they 

 are often of a highly complex character. 



Our next task is then to investigate the processes by w^hich these 

 characteristics have arisen. The problem is parallel — perhaps 

 rather identical — with that which the student of structure sets 

 himself when he asks how it happens that the animal possesses 

 certain complex adaptive structures that are inherited from its 

 progenitors. We cannot hold that complex characteristics can 

 arise without any processes leading to them, unless we are pre- 

 pared to abandon the scientific method Where shall we look for 

 the processes giving rise to characteristics that do not take origin 

 in the lifetime of the present individual ^ 



Clearly, there is but one possibility here. What we call the 

 '* individual life" is not the entire history of this mass of matter 

 and energy that we call "an animal." It has existed for number- 

 less ages in connection with other individuals, as "germ cell," 

 or the like. Since the animal becomes modified and adapted in 

 accordance with certain physiological laws, even in the brief span 

 of its individual life, it is evident that the unmeasured ages of its 

 previous existence could hardly pass without the occurrence of 

 processes of modification. And it is only in this period that the 

 processes could have occurred which have given it the complex 

 inherited characteristics that it now has. We have then no alter- 

 native but to study the nature of these processes, if we wish to 

 understand the origin of the characteristics under discussion. 



Such a study of the processes by which organisms become modi- 

 fied in the life history of the race is of course as much a part of 

 physiology as is the study of the processes of metabolism, and it 

 must be pursued in the same spirit. Most of the existing science 

 of physiology deals with the rapid processes taking place in the 

 lifetime of the individual and in its "body." But of course the 

 slower processes occurring in the germ material and resulting in 

 modifications which become apparent in later generations are proc- 

 esses occurring in space and time, and open to objective experi- 



