PARAMECIUM 79 



the normal stream of life processes may produce negative or 

 positive reactions, according as they are usually followed by 

 changes that are injurious or beneficial. (5) Whether a given 

 change shall produce reaction or not often depends on the com- 

 pleteness or incompleteness of the performance of the metabolic 

 processes of the organism under the existing conditions. This 

 makes the behavior fundamentally regulatory " (62, p. 299). 



Heredity in Paramecium. Most of the complex phenomena 

 of life are exhibited by the one-celled animals, and it is not strange 

 to find that the offspring of the Protozoa resemble their parents. 

 This " resemblance of child to parent" (51, p. 309) is called heredity. 

 The descendants of a living organism are not exact copies of the 

 progenitor, but differ in various minor details; " the difference 

 between child and parent is called variation "(51, p. 309). Para- 

 mecium has been made the subject of a thorough test with regard 

 to hereditary phenomena by Professor Jennings (65). This in- 

 vestigator studied and measured over ten thousand Paramecia 

 which were carefully bred in the laboratory. In a " wild " lot 

 of Paramecia eight distinct races were found. Each race con- 

 sisted of individuals, which, though affected by their environment, 

 maintained a certain average size which was inherited. Charac- 

 teristics that were acquired by the Paramecia were not handed 

 down to their offspring, but were lost when the animals were 

 reorganized during reproduction. It is thus the " fundamental 

 constitution of the race," and not the various external influences 

 which determine the characteristics of each new generation. 



