THEORY OF EVOLUTION 



181 



ment with hooded rats fails entirely to estab- 

 lish his contention of change in potency of the 

 germ or of contamination of factors, while on 

 the contrary they are in entire accord with the 

 view that he is dealing with a case of modify- 

 ing factors. 



Equally important are the results that Jen- 

 nings has obtained with certain protozoa. Par- 

 amecium multiplies by dividing across in the 



FIG. 89. Races of Paramecium. (After Jennings.) 



