HEREDITY IN THE PROTOZOA 287 



"the difference produced by selection continued to 

 exist after conjugation." It appears that some kind 

 of change had been produced, and that the change 

 in rate was inherited after selection ceased. 



More recently still Jennings (1916) has carried 

 out an elaborate experiment with another Protozoan, 

 Difflugia corona (Fig. 66). This form also shows 

 ''in nature" great variability, due, it appears, to 

 several or to many races often existing in the same 

 locality. If any individual is taken as the starting 

 point for a new population, it is found that the 

 fission line that results is composed of individuals 

 that are more like the parent than like members of 

 the wild population taken as a whole. In other 

 words each individual tends to transmit its peculi- 

 arities to its offspring. Fig. 67. Jennings then 

 showed that selection within a pure line, i.e., in a 

 population descended from a single individual by 

 fission, brings about a change in the direction of 

 selection and that this change remains at least for a 

 time after selection ceases. 



The characters that were examined included the 

 number of spines, the length of the si)ines, the 

 diameter of the shell, the depth of the shell, the 

 number of s]:)ines around the mouth, tlie diameter 

 of the mouth. Through selection many diverse 

 lines were produced in a strain coming from one 

 original individual. The selection was based not 

 only on individual differences, but also on ''past 

 performance." 



Selection was often made ijy i)icking out extreme 



